Make :SearchNotes work properly without vim-shell (fixes #53)

This follows the initial suggestion of removing the try/catch construct.
I still haven't a clue what the hell is going on here, but I'm done
fighting Vim (script) and just want this to work now! :-)

Add lots of debug logging (related to issue #53)

Document issue #53 in the README

As suggested by @canpolat:
#53 (comment)

Release changes to search-notes.py as vim-notes 0.33.1 (issue #53)

Enable showing code block markers

Fixes #107

Merge pull request #104: Make concealing configurable

I made a few changes while merging this pull request:

1. I changed the logic inside syntax/notes.vim to use the function
   xolox#misc#option#get() with a default option value of true (1). In
   my mind this makes a lot more sense than checking for the existence
   of variables without checking their actual values.

2. I renamed notes_conceal_italics to notes_conceal_italic to be
   consistent with the other options (IMHO).

3. I rewrote the documentation additions because A) doc/notes.txt is
   generated from README.md so the changes by @naddeoa would have gone
   lost and B) because there were typos in the additions
   (s/coneal/conceal/g).

4. The documentation for notes_conceal_code was incorrect because
   the code changes by @naddeoa only apply to the markers for inline
   code fragments, not the markers for multi line code blocks. I kept
   the implementation as is and updated the documentation to match the
   implementation.

See also pull request 104 on GitHub:
  #104

Fix issue #102: Code block detection seems somewhat broken

See issue 102 on GitHub:
  #102

Thanks to @gstewart for the analysis.

Easy customization of new note template (also from command line)

This was added to enable simple integration with
tools like sup (https://github.com/ceocoder/sup)

Merge pull request #103: Open HTML in split & Mediawiki converter

In this merge commit I'm making a couple of minor changes:

 - The `---` sequence is now used as a horizontal divider in the
   Mediawiki syntax converter.

 - The changes to xolox#notes#html#view() created a temporary file even
   when the HTML was shown in a Vim split window, now the temporary file
   is only created when it needs to be passed to a web browser.

 - I changed some wrong indentation, removed some unused code (the
   counter variable) and renamed some private variables
   (s/hilight/highlight/g) and added word boundaries to the
   TODO/DONE/XXX matching in the file mediawiki.vim.

 - No trailing empty lines are added when a note is converted to
   Mediawiki syntax (there were in the pull request, but without context
   or explanation so I'd rather keep the Markdown, HTML and Mediawiki
   converters consistent).

Merge pull request 98: Accept ``` code markers (similar to GFM*)

* GFM -> GitHub Flavored Markdown