Docs update - 4.8.0-beta00007 changes

[Shazwazza]

Lots of changes here (still a WIP)

• Updates docs home page with up to date list of packages and links
• Updates api docs Toc with up to date list of packages
• Ensures that all converted package.md files for each namespace are included in the docs, previously this was not the case
• Ensures there are correct headers/titles for non-namespace overview.md files (such as Lucene.Net, Lucene.NetAnalysis.Common, etc...)
• Much better handling of namespace detection for package.md files
• One sln file to manage the documentation tools
• Updates website docs links to point to new docs URLs with versions (i.e. http://lucenenet.apache.org/docs/4.8.0-beta00007)
• Get the TestFramework project docs working
• Add lucene in action books and links in docs site https://www.amazon.com/s?k=lucene&ref=nb_sb_noss_1 (and/or on the website too)
• Fix download page "Be sure to check out the download page documentation. We are supposed to be linking to Apache's mirrors, as the repo is not setup for high traffic volume: http://www.apache.org/dev/release-download-pages.html"
• updates code snippet on homepage, see Updates docs build #229 (comment)
• Git branch per docs release - so the Improve this doc works
• deal with @lucene.experimental tags in places it's not working (i.e. conceptual files, override files and others)

(There's more stuff i'll add here, just need to remember it all)