use gob instead of manual marshalling

this removes the need for messaging tests
update client to use gob
Merge pull request #98 from lukechampine/node

Switch messaging marshalling to gob
initialize TCPServer struct directly
add rpcnetwork
add data package

the data package contains structs and methods for sectors and
segments, as defined in #67.
move client to RPC
use common/data in client
move data to common
use Sector in erasure
update client for new encoding API
use []byte in place of string