Update third-party libraries for benchmark

[MasterOdin]

PR updates @msgpack/msgpack to the latest version, as well as adds the msgpackr library to the benchmark. I was mostly looking to understand some bottlenecks I'm seeing in a socket.io based application, and possible ways to improve throughput (such as replacing notepack.io in socket.io), but figured useful to maybe have this here for future readers.

[darrachequesne]

@MasterOdin thanks :rocket: