Add dump template func for debugging

[bep]

See https://github.com/sanity-io/litter

The output is great (as below from a random test), but may be "too much" even for the advanced user:

&hugolib.Page{ // p0
  pageInit: &hugolib.pageInit{},
  Kind: "home",
  Pages: nil,
  Params: map[string]interface {}{
    "draft": false,
    "expirydate": time.Time{},
    "iscjklanguage": false,
    "lastmod": time.Time{},
    "outputs": output.Formats{ // p1210
      output.Format{
        Name: "JSON",
        MediaType: media.Type{
          MainType: "application",
          SubType: "json",
          Suffix: "json",
          Delimiter: ".",
        },
        Path: "",
        BaseName: "index",
        Rel: "alternate",
        Protocol: "",
        IsPlainText: true,
        IsHTML: false,
        NoUgly: false,
        NotAlternative: false,
      },
    },
    "publishdate": time.Time{},
    "title": "JSON Home",
  },
  Content: "\n\n<h1 id=\"doc\">Doc</h1>\n\nShortJSON\n\nOtherShort: <h1>Hi!</h1>\n",
  Summary: " Doc ShortJSON OtherShort: Hi! ",
  TableOfContents: "<nav id=\"TableOfContents\">\n<ul>\n<li><a href=\"#doc\">Doc</a></li>\n</ul>\n</nav>",
  Aliases: nil,
  Images: nil,
  Videos: nil,
  Truncated: false,
  Draft: false,
  Status: "",
  PublishDate: time.Time{},
  ExpiryDate: time.Time{},
  PageMeta: hugolib.PageMeta{
    Weight: 0,
  },
  Markup: "markdown",
  Layout: "",
  Source: hugolib.Source{
    Frontmatter: nil,
    Content: nil,
    File: source.File{
      Contents: nil,
    },
  },
  Position: hugolib.Position{
    Prev: nil,
    Next: nil,
    PrevInSection: nil,
    NextInSection: nil,
  },
  GitInfo: nil,
  Site: &hugolib.SiteInfo{
    Taxonomies: hugolib.TaxonomyList{ // p34
      "categories": hugolib.Taxonomy{
      },
      "en": hugolib.Taxonomy{
      },
      "tags": hugolib.Taxonomy{
      },
    },
    Authors: hugolib.AuthorList{
    },
    Social: hugolib.SiteSocial{ // p1204
    },
    PageCollections: &hugolib.PageCollections{ // p35
      Pages: hugolib.Pages{
        p0,
      },
      AllPages: hugolib.Pages{ // p687
        p0,
        &hugolib.Page{ // p1
          pageInit: &hugolib.pageInit{},
          Kind: "home",
          Pages: nil,
          Params: map[string]interface {}{
            "draft": false,
            "expirydate": time.Time{},
            "iscjklanguage": false,
            "lastmod": time.Time{},
            "outputs": output.Formats{ // p1202
              output.Format{
                Name: "JSON",
                MediaType: media.Type{
                  MainType: "application",
                  SubType: "json",
                  Suffix: "json",
                  Delimiter: ".",
                },
                Path: "",
                BaseName: "index",
                Rel: "alternate",
                Protocol: "",
                IsPlainText: true,
                IsHTML: false,
                NoUgly: false,
                NotAlternative: false,
              },
            },
            "publishdate": time.Time{},
            "title": "JSON Nynorsk Heim",
          },
          Content: "\n\n<h1 id=\"doc\">Doc</h1>\n\nShortJSON\n\nOtherShort: <h1>Hi!</h1>\n",
          Summary: " Doc ShortJSON OtherShort: Hi! ",
          TableOfContents: "<nav id=\"TableOfContents\">\n<ul>\n<li><a href=\"#doc\">Doc</a></li>\n</ul>\n</nav>",
          Aliases: nil,
          Images: nil,
          Videos: nil,
          Truncated: false,
          Draft: false,
          Status: "",
          PublishDate: time.Time{},
          ExpiryDate: time.Time{},
          PageMeta: hugolib.PageMeta{
            Weight: 0,
          },
          Markup: "markdown",
          Layout: "",
          Source: hugolib.Source{
            Frontmatter: nil,
            Content: nil,
            File: source.File{
              Contents: nil,
            },
          },
          Position: hugolib.Position{
            Prev: nil,
            Next: nil,
            PrevInSection: nil,
            NextInSection: nil,
          },
          GitInfo: nil,
          Site: &hugolib.SiteInfo{
            Taxonomies: hugolib.TaxonomyList{ // p688
              "categories": hugolib.Taxonomy{
              },
              "en": hugolib.Taxonomy{
              },
              "tags": hugolib.Taxonomy{
              },
            },
            Authors: hugolib.AuthorList{
            },
            Social: hugolib.SiteSocial{ // p1196
            },
            PageCollections: &hugolib.PageCollections{ // p689
              Pages: hugolib.Pages{
                p1,
              },
              AllPages: p687,
              RegularPages: nil,
              AllRegularPages: nil,
            },
            Files: &nil, // p1197
            Menus: &hugolib.Menus{ // p691
            },
            Hugo: nil,
            Title: "Tittel på Nynorsk",
            RSSLink: "http://example.com/blog/index.xml",
            Author: map[string]interface {}{ // p1199
            },
            LanguageCode: "",
            DisqusShortname: "",
            GoogleAnalytics: "",
            Copyright: "",
            LastChange: time.Time{},
            Permalinks: hugolib.PermalinkOverrides{ // p1200
            },
            Params: map[string]interface {}{ // p690
              "languagename": "Nynorsk",
              "title": "Tittel på Nynorsk",
              "weight": 2,
            },
            BuildDrafts: false,
            Data: &map[string]interface {}{ // p43
            },
            Language: &helpers.Language{ // p40
              Lang: "nn",
              LanguageName: "Nynorsk",
              Title: "Tittel på Nynorsk",
              Weight: 2,
              Cfg: &viper.Viper{}, // p39
            },
            LanguagePrefix: "/nn",
            Languages: helpers.Languages{ // p41
              &helpers.Language{ // p38
                Lang: "en",
                LanguageName: "English",
                Title: "Title in English",
                Weight: 1,
                Cfg: p39,
              },
              p40,
            },
          },
          Title: "JSON Nynorsk Heim",
          Description: "",
          Keywords: []string{} // p3
,
          Data: map[string]interface {}{
            "Pages": nil,
          },
          Date: time.Time{},
          Lastmod: time.Time{},
          Sitemap: hugolib.Sitemap{
            ChangeFreq: "",
            Priority: -1,
            Filename: "",
          },
          URLPath: hugolib.URLPath{
            URL: "/",
            Permalink: "",
            Slug: "",
            Section: "",
          },
        },
      },
      RegularPages: nil,
      AllRegularPages: nil,
    },
    Files: &nil, // p1205
    Menus: &hugolib.Menus{ // p42
    },
    Hugo: nil,
    Title: "Title in English",
    RSSLink: "http://example.com/blog/index.xml",
    Author: map[string]interface {}{ // p1207
    },
    LanguageCode: "",
    DisqusShortname: "",
    GoogleAnalytics: "",
    Copyright: "",
    LastChange: time.Time{},
    Permalinks: hugolib.PermalinkOverrides{ // p1208
    },
    Params: map[string]interface {}{ // p36
      "languagename": "English",
      "title": "Title in English",
      "weight": 1,
    },
    BuildDrafts: false,
    Data: &p43, // p1209
    Language: p38,
    LanguagePrefix: "",
    Languages: p41,
  },
  Title: "JSON Home",
  Description: "",
  Keywords: p3,
  Data: map[string]interface {}{
    "Pages": nil,
  },
  Date: time.Time{},
  Lastmod: time.Time{},
  Sitemap: hugolib.Sitemap{
    ChangeFreq: "",
    Priority: -1,
    Filename: "",
  },
  URLPath: hugolib.URLPath{
    URL: "/",
    Permalink: "",
    Slug: "",
    Section: "",
  },
}

[moorereason]

I'd be in favor of a general dump template function.

[kaushalmodi]

may be "too much" even for the advanced user

That might be alright is user can specify what they want to be printed. Assuming that the template fn name is dump, may be:

{{ dump .Params }} <!-- Print Page Params when called from a page template -->
{{ dump .GitInfo }} <!-- should also work for structs -->
{{ dump .File }}

I gave the above examples because I ended up creating something like dump but with whatever was available in user-land.. also printing structs needs the user to know the exact elements at the moment.

PS: The .File object is a special PITA as discussed on discourse.