New msgpack implementation

[dmcgowan]

I mark this as a work in progress since it is not ready to be merged. The code design may be reviewed since I plan on using this structure.

Includes:

• Different msgpack implementation
• New raw message type
• New extension implementation

What this enables:

• More efficient proxying
• Zero copy in-memory channels
• Partial Decoding
• Sending/receiving non struct/map objects

[mcollina]

:+1: and congrats on the new msgpack impl! IMHO, that should live in its own repo, it is worth using independently of libchan.

[dmcgowan]

@mcollina I will likely split it out later, I wanted it at least reviewed as a whole first since the libchan changes are in lockstep.

[dmcgowan]

This is now a working implementation with full unit test passing. Still going to increase coverage for the new library and updated implementation.

[dmcgowan]

Pushed an update with the msgpack changes split out. I submitted upstream but until then my fork will need to be used (https://github.com/dmcgowan/msgpack/tree/raw-message), use the raw-message branch until I get it onto master.

[dmcgowan]

The msgpack fork has been cleaned up and this PR is ready to merge. Any additional changes and refactoring to libchan should be done on top of this change.

Ping @stevvooe @BrianBland for a chance to review

[dmcgowan]

Also removed dead code related to registering and encoding raw connections. This is unused and unspecified. Rather than porting the logic, much of the code was commented out. Now it is completely removed.

[dmcgowan]

Closing to see if reopen will enable circlci

[dmcgowan]

Re-creating PR for new CI integration and code review