Handle multiple RPCs on the same stream

[jteplitz]

Currently we open a new TCP connection for each RPC. This works, but it's worth looking into reusing connections. We should hold off on this until we've implemented most of the protocol though because then we can see how much reuse is necessary.

[jteplitz]

We'll also want an easy way to time out an RPC so we can resend it. Right now we're dependent on the TCP timeout.

[jteplitz]

Blocked on #7 since our current shutdown hack basically makes this impossible until we have an async server