VimeoIE: allow to download password protected videos
YoutubeIE: Detect new Vevo style videos

The url_encoded_fmt_stream_map can be found in the video page, but the signature must be decrypted, we get it from the webpage instead of the `get_video_info` pages because we have only discover the algorithm for keys with both sub keys of size 43.
Detect more vevo videos
Move the decrypting function to a static method
YoutubeIE: report warnings instead of errors if the subtitles are not found (related #901)

For example when downloading a playlist some videos may not have subtitles but the download shouldn't stop.
README: Add brief description for manpages/apropos.

Trying to mimic the manpage of (GNU) `ls`, we don't conjugate the verb as
"downloads" or something else.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
Change metavar of "--sub-format" from LANG to FORMAT
GenericIE: look for Open Graph info

Only if there is a direct link to the file, don't try if it points to a Flash player
added StatigrIE
added StatigrIE
added test for Statigr
Merge pull request #905 from rbrito/manpage-apropos

README: Add brief description for manpages/apropos.
Merge remote-tracking branch 'yasoob/master'
Improve Statigr.am IE
Improvge error reporting
Merge remote-tracking branch 'origin/vimeo_passworded_videos'
[Statigr.am] Correct uploader id
Merge remote-tracking branch 'jaimeMF/vevo_fix'
added an IE and test for break.com
Use new signature calculation method only if sig is not present