CapnP' Cerealization and IPC

[itdaniher]

The current plan is to have a final-level sink / tail that handles IPC via Unix domain socket in its own task, sending CapnP serialized messages. Python will then append these messages to a log file, push them to a browser via websockets(?), and do math(?).

The schema's been written, capnp-rust docs have been read, and rust IPC socket docs have been read, but Ian needs to actually sit down and write some code. This is slightly blocked by #5.

/cc @madisonmay

[itdaniher]

Dropped Capnp in favor of msgpack, which provides less overhead and a simpler serialization schema. Dropped unix IPC for TCP, as unix sockets are blocked by rust-lang/rust#12103. Code needs a bit of touchup (funnel to instant.rs,) but basic structure is a-ok.