Allows to use markdown tables, automatic table of contents and HTML

This patch will allow to embed tables, generate automatic table of contents and add custom HTML within Markdown. Documentation is also updated accordingly.

I tested the code with Travis: https://travis-ci.org/#!/Anthony-Gaudino/gitlabhq/builds/2614387
Merged the feature branch with Master before testing, so test was made with the change.


Here is an example image:
http://www.freeimagehosting.net/p7dyx

And here is the source:
http://pastebin.com/vHKpyvza

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Commit 32657a5b7a4075a5a0505ebd36e41bb1459f47f5 will make ~toc~ only work if placed on first line of content, so if for whatever reason there's a ~toc~ in the content it will not trigger the TOC feature.