0.3.0: BREAKS PROTOCOL BACKWARD COMPATIBILITY

This version is not compatible with versions prior to 0.3.0, so
'git pull' and restart if you are following the alpha.

Changes from 0.2.5:

 - All multicast frames are now signed by the original sender. This
   will permit very efficient and fault tolerant rate limitation
   across networks, and imposes a kind of "hash cash" cost on those
   who wish to flood the network by forcing them to keep regenerating
   new identities.

 - Simplified peer last unicast / last multicast accounting.

 - Improvements to multicast propagation algorithm to achieve better
   coverage with less redundant messages.

 - The bloated Switch class went on a diet, having packet decoding
   broken out into PacketDecoder and multicast propagation algorithm
   broken out into Multicaster.

 - Multicaster is implemented as a template mockable class to permit
   future simulations of huge scale multicast using the actual code
   instead of mockups in another language.

 - Introduced a faster non-cryptographic random source for things
   like multicast propagation and address choosing.

 - Some code cleanup, removal of outdated comments, etc.
Also exclude upstream when picking supernode for multicast propagation, to not bounce back and forth to the same supernode.
Small updates to documentation, a few precautionary fixes.
Filter work, adding toString() and main evaluation function.