Also:
- Parse targets on startup and catch badly formed ones before Scope can start.
- If no port is specified, use default port for scheme; if no scheme is specificed, use 4040.
- Use username as probe token

- Add interfaces to allow for alternative implementations for Collector, ControlRouter
  and PipeRouter.
- Pass contexts on http handlers to these interfaces.  Although not used by the current
  (local, in-memory) implementations, the idea is this will be used to pass headers to
  implementations which support multitenancy (by, for instance, putting an authenticating
  reverse proxy in form of the app, and then inspecting the headers of the request for
  a used id).

* New encoding format:
  * Msgpack reports between probe<->app (smaller representation, faster to
    encode/decode).
  * Still use JSON between app<->UI (try to avoid making javascript deal with
    mspack).

  The app still suports publishing reports in both gob and JSON, not braking
  backwards compatibility.

* Use compile-time generated marshallers/unmarshallers for higher performance. In
  order to be able to skip code-generation for certain types, I included
  https://github.com/2opremio/go-1/tree/master/codec/codecgen instead of
  upstream until https://github.com/ugorji/go/pull/139 is merged.

* Encode/decode intermediate types using github.com/ugorji/go/codec.Selfer
  for higher performance and reducing garbage collection (no temporary buffers).

- Add store of pipes in the app
- Add pipe type, handling impedance mismatch, used in app and probe.
- App <-> Probe pipes have their own websockets.
- Add pipe websocket endpoint in app.
- Pipe IDs are strings, lose the request/response IDs, and give the json encoder lowercase field names.
- Add simple golang ws client, for testing.
- Pipe lifecycle plumbing.
- Ref count and timeout both ends of pipes in the app
- Deal with POST /api/pipe/:pid?_method=delete
- Add end-to-end unit test for pipes.
- Add test for timing out pipes.
- Update go-docker client to tomwilkie/go-dockerclient
- Backend work for non-raw ttys
- Close pipes when they close themselves in the probe
- Ensure all http connections are done before returning from client.Stop()