Clarify that download rate is in bytes per second

I found https://github.com/rg3/youtube-dl/commit/f918ec7ea29a37521d1fc22fb9f900283c5a2c49 but it is still not clear to anyone who hasn't read Issue #723 whether the limit is in bits or bytes.  This is doubly confusing because 1) ISPs usually advertise speeds in bits per second, and 2) lowercase "k" and "m" are often used in correlation with bits rather than bytes.
Extractor for websurg.com
Merge remote-tracking branch 'upstream/master' into websurg
Improvements
Changes suggested by @phihag
Unused variable
Use self._download_webpage everywhere
Implement format selection in YoutubeDL

Now the IEs can set a formats field in the info_dict, with the formats ordered from worst to best quality. It's a list of dicts with the following fields:
* Mandatory: url and ext
* Optional: format and format_id

The format_id is used for choosing which formats have to be downloaded.

Now a video result is processed by the method process_video_result.
Implement the max quality option in YoutubeDL
Do not handle format selection for IEs that already handle it
Default 'format' field to {width}x{height}

If width is None, use {height}p and if height is None, '???'
Implement the prefer_free_formats in YoutubeDL
Fix the default values of format_id and format
Don't set the '-aq'  option with the opus format (fixes #1263)
FFmpegPostProcessor: print the command line used if the --verbose option is given
add support for NowVideo.ch
Add support for single-test tox runs

Use a sintax like
    tox test.test_download:TestDownload.test_NowVideo
to run the specific test on all the tox environments (Python versions)
Add an extractor for internetvideoarchive.com videos

It's used by videodetective.com
Add an extractor for videodetective.com (closes #262)

It uses the internetvideoarchive.com platform.
Add an extractor for rottentomatoes.com and improve InternetVideoArchiveIE to get the best quality