Add RecordIO parsing

[oubiwann]

The scheduler sends results in RecordIO format (I think this is from Go? It's used internally at Google, and they haven't released a standalone library yet). We need to be able to parse that.

Files/URLs of potential interest:

• https://github.com/google/or-tools/blob/master/src/base/recordio.h
• https://issues.apache.org/jira/browse/MESOS-3566
• https://issues.apache.org/jira/browse/MESOS-3562
• https://reviews.apache.org/r/39452/diff/2#0

The last bullet provides example Python which has since been converted to pseudo code on the HTTP docs site.

Related commit to protobuf:

• https://github.com/google/protobuf/commit/bd9bfe9a93999e67d4638a0ed18110c1446d0468

[oubiwann]

Okay, I've got a protocol extending a java.io.InputStream that addresses this. PR incoming ...