Adding an IPC mechanism

This is to fix #41 and #24. Previously the Serf CLI used an RPC mechanism using Go's net/rpc with Gob encoding. This is rather difficult to use across platforms, so instead we now use a simple MsgPack over TCP mechanism. The same RPC address is used, but now it can be a well documented format that other applications can make use of. Additionally we expose the `Monitor` and `Stream` mechanisms to provide a low-latency streaming mechanism for event handling.