Collectors hold recent reports in memory.
When querier needs 'live' data, fetch it from collectors instead
of from the long-term store.
Send reports from collector to querier in msgpack; disable compression
on REST call, otherwise Go silently decompresses, which takes longer.
Typically this means the http caller has closed the connection,
so no point responding to them.
Also check at the point we send a response back, and log to OpenTracing.
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).
