Add basic mkdocs override code.
Normalize docroot in GitHub URL
Autogen mkdocs overrides
Clean up mkdocs builder and search
Merge branch 'mkdocs-overrides'

Conflicts:
	readthedocs/doc_builder/backends/mkdocs.py
Update RTD mkdocs theme
Install mkdocs into all virtualenvs
Include page name in mkdocs headers
Clean up task build output
Clean up mkdocs builder
Bump theme
Remove GTD for now
Merge branch 'mkdocs'
Don’t generate pages dict for now.
Kill overrides
Add wheels for Python 3 and mkdocs
Fix RTD TOC on mkdocs
Update RTD mkdocs footer
Copy mkdocs json properly.
Hack search URL for now