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
Add CinemassacreIE
[CinemassacreIE] Add support for other embed methods
[CinemassacreIE] Remove docstring from class
[CinemassacreIE] Use MD5 to check in TEST description
add capability to suppress expected warnings in tests
add tox configuration file for easy testing
[fixup] remove unnecessary commented function
Merge remote-tracking branch 'origin/tox'
Add basic --download-archive option

Often, users want to be able to download only videos they haven't seen before, despite the video files having been deleted or moved in the mean time.
When --download-archive FILE is given, the extractor and ID of every download is recorded in the specified file. If it is already present, the video in question is skipped.
Move try_rm to test helpers
Allow users to specify an age limit (fixes #1545)

With these changes, users can now restrict what videos are downloaded by the intented audience, by specifying their age with --age-limit YEARS .
Add rudimentary support in youtube, pornotube, and youporn.
[viddler] Add basic support (Fixes #1520)
release 2013.10.06