Ignore the dash build dir.
Render the Dash feed files and show them on the download page.

See http://kapeli.com/hostfeed/ for more information.
Merge branch 'master' into dash-feeds

Conflicts:
	readthedocs/doc_builder/backends/sphinx_dash.py
	readthedocs/projects/models.py
	readthedocs/projects/views/public.py
Removed a left over from debugging and handle protocol relative URLs in the Dash feed files correctly.
Added i18n to download page template and reformatted the HTML a bit.
Fixed a line length issue.
Merge branch 'dash-feeds'