Import `rust-jsonrpc` here

[tcharding]

This repo is going to move to rust-bitcoin org soon-ish. Before doing so lets import rust-jsonrpc into this repo then the repo hold all the crates that we (Andrew and I) do not really enjoy working on feel bound-by-honour to provide and maintain for the community.

[tcharding]

This issue is here as an artefact so that the reasoning is documented and the import doesn't later look like just some madness that I did.

@apoelstra please concept-ack the move and the ack if you want the claim that includes your name.

[apoelstra]

concept ACK. We should move rust-jsonrpc. Let me get apoelstra/rust-jsonrpc#119 in first.

[tcharding]

Note #14

[tcharding]

Done in #19.