Move readme in docs/

* Move content in Markdown
* Local reading simplified
* Easy to edit .md
* GitHub integration

Update table of contents

Fix links in TOC

Fix links to docs

readme.html

Rename + reword links

Older PHP-markdown for compat with older PHP versions

Rename TOC
Merge pull request #1391 from YOURLS/LeoColomb-Feature-Docs

Move readme in docs/