Add initial sphinx docs

With an initial guide for using youtube_dl from python programs.
Add an option to specify custom HTTP headers
toypics.net support
Merge remote-tracking branch 'fiocfun/toypics-support'
[toypics] Separate user and video extraction (#2601)
Remove unused imports and clarify variable names
[pornhub] Fix uploader extraction and extract counts
[xtube] user playlist extractor
[metacafe] Modernize
[metacafe] Replace cbs test
[metacafe] More modernize
[metacafe] Remove accidently inserted comment string
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