Streaming - Experimental Support

[mmmries]

This is a first second third pass at streaming support. It follows a pattern of using get_statem process that finds a gnat connection, tries to register itself and then monitors the connection so that it can reset the state machine if the connection dies.

For example, here is a state diagram for a subscription

In future PRs I'm imagining a higher-level supervisor that will automatically setup the connection, streaming client and subscribers by adding a single supervisor to a user's app.

[mmmries]

I was feeling stuck with how to release this additional support when I am still very un-sure of whether this is the right API I was users to use, so I've decided to close this PR and start a separate gnat_streaming package that will handle all things streaming. That way I can release that as a 0.0.1 version and make it very clear that it is a alpha/beta version of the code