Embedding API

[rubiojr]

Highlights:

• Exposes a new reactor package (not particularly attached to this name) .
• Doesn't change existing API.

This makes it easier to:

• Embed Beehive's in other binaries or libraries.
• Create custom Beehive binaries with additional hive packages hosted elsewhere.
• Create specialized binaries which benefit from Beehive's vast catalog of bees, making it possible to create really powerful interactions with a few lines of code.

Clients embedding Beehive's don't have a built-in HTTP API server started by default, which is probably desirable and safer if you're programming your own chains, as opposed to using the GUI to create them.

I've included an example that demonstrates embedding. Also implemented the Hello bee action the example is using.

In future iterations, we could expose an interface to start/stop the API server also, maybe add a few functions that wrap the event, action and chain creation while adding some safety.

[rubiojr]

A slightly more complex example that demonstrates using an out-of-tree bee in an external repo: https://github.com/rubiojr/commit-monitor

[coveralls]

Coverage remained the same at 72.705% when pulling e098b31 on reactor into f8fd3de on master.