Support TCP

[stephenmathieson]

seems like the only difference between this and https://github.com/segmentio/jsonrpc.js is protocol support

we could do something like:

const { protocol } = url.parse(address)
if (protocol === 'tcp') {
  this.request = this.makeTCPRequest.bind(this)
} else {
  this.request = this.makeHTTPRequest.bind(this)
}