* replaced explicit NACKs and numACKs with ACK bitfields for high congestion links

* increased the maximum number of fragments allowed in a message from 31 to 127,
  reducing the maximum fragment size to 8KB and moving around some bits in the fragment
  info.  This is not backwards compatible.
* removed the old (hokey) congestion control description, replacing it with the TCP-esque
  algorithm implemented
note: the code for the ACK bitfields and fragment info changes have not yet been
implemented, so the old version of this document describes whats going on in the live net.
the new bitfields / fragment info should be deployed in the next day or so (hopefully :)