Small refactoring to aid approachability

[dazoakley]

• Separate out nested classes in non-obvious locations.
• Move spec files around so it's a little more clear what they're representing.
• Introduce a couple of module files to load child classes.
• Make it so consuming code only needs to require "alephant/broker" to get going.

[Integralist]

One comment, but otherwise happy with the refactor

[dazoakley]

@Integralist you happy for this to go in?

[Integralist]

👍