So we save space writing out empty topologies.
Need to fix up `app_client_internal_test.go` to use Scope's
`test/reflect` package that understands empty==nil, so now it doesn't
need a previous workaround.
Remove a similar workaround in `probe_internal_test.go` that isn't
necessary since it's already using that package.
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
* 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).
