Release 0.6 cleanup

This closes #26, and #32, in addition to the other new features.

I'm planning to push the release tomorrow.  From the Readme:

  - **BACKWARDS-INCOMPATIBLE** Reworked Client constructor to take API key and
    optional Faraday configuration block.  See 9045ffc for details.
  - Migrated documentation to YARD
  - Provide basic response wrappers specific to generic request types.
  - Raise Exceptions on error response from Orchestrate API.
  - Remove custom logger in favor of the option to use Faraday middleware.
  - Accept Time/Date objects for Timestamp arguments to Event-related methods.

The backwards-incompatible change to the Client constructor was, I feel, eventually necessary and desirable.  We've gotten rid of another unnecessary class (Config), and aren't artificially keeping track of a global in the "default".  The client will need to be instantiated during an application's setup, and stored somewhere, similar to how the [Ruby Redis](https://github.com/redis/redis-rb) library works.  

An advanced rubyist will know what to do – The client is an entrance to something else, and they'll cache it in a module's constant or something.  A newbie might hae more trouble – they'll want to treat it like an ActiveRecord class that's effectively a hidden "global" into their database.

This approach is more flexible, lends itself to someone interfacing with multiple Orchestrate Applications in the same code easily (try _that_ with ActiveRecord sometime), and with the next release I'm planning a much richer class-system based around `Orchestrate::Application`, and there will be facilities for having a "default" application in this manner.