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
[generic] Run TED detection before JW Player detection

Otherwise it overwrittes the `mobj` variable.
[videolectures.net] Make description optional
itag 160 is 144p, not 192p
Make missing test definition fields an error

If the result is not testable (for example, because a description changes often), either pass in a type or a regular expression (a string starting with 're:')
Merge remote-tracking branch 'hurda/patch-1'
[youtube] Remove useless resolution fields from format definitions

These can be - and are - calculated automatically by the YoutubeDL core.
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