- clean up this script, merge relevant resman/scripts/bwlimit

- clean up this script, merge relevant resman/scripts/bwlimit
  functionality into here
- add tons of documentation, and fix a minor (haha) bug: tc reports
  minor class numbers in hexadecimal, not decimal. Fix things so that it
  works with VNET, which classifies packets from xid 500 into class
  1:1f4, *not* 1:500.
- set the "default" minor class number to ffff to emphasize this point.
- VNET now classifies packets, no need for class filters
- don't override cburst, let tc decide what it should be, which sounds
  reasonable. At least until we figure out if burst lengths should be
  related to shares.
- make everything just a whole lot nicer to use