Add initial sphinx docs

With an initial guide for using youtube_dl from python programs.
Add an option to specify custom HTTP headers
[xtube] user playlist extractor
Merge remote-tracking branch 'fiocfun/xtube-user-extractor'
[worldstarhiphop] Modernize
[xbef] (Add extractor)
[utils] Simplify setproctitle
[test] Move expect_info_dict out of test_download
[instagram] Add support for user profiles (Fixes #2606)
release 2014.03.23
[extractor/common] Clarify preference key in formats
[radiofrance] Modernize
Merge pull request #2567 from jaimeMF/sphinx-docs

Add initial sphinx docs
[instagram] Fix info_dict key name
[RTS] Add extractor (Fixes #2608)
Merge remote-tracking branch 'origin/master'
release 2013.03.24
[soundcloud] Simplify string literals
[soundcloud] Always add streaming formats
release 2013.03.24.1