Merge pull request #99 from lukechampine/rpc

RPC and Sectors
make RPC the default
pass a message router to up/download
make SendMessage a method of RPCServer
make zeronetwork implement MessageRouter
update server for RPC
RPC overhaul of State

Using RPC alters how State operates in a few key ways. The good
news is that these changes almost uniformly result in cleaner,
simpler code. state_test.go is a little uglier because type
assertions are required now, but that's about the only down side.
update consensus for RPC
remove TCP code