Also:
* Remove Gob encoder/decoder
* Stop using custom encoders/decoders for Timestamps (both ugorji and the Golang JSON codecs use nanosecond precision).
* Use idiomatic way to check for existence in metric.LastSample()
* 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).
