Eventually rework how Designs are specified

[sarahzrf]

I'd like to eventually rework Designs to be declared using a method-based DSL instead of directly as data structures - this will make it both easier to document the options available in them, and make mistakes in their definitions result in errors instead of silently passing.

[sarahzrf]

Current plans: Have them work like Rack apps with Builder. A new-style Design will be an object with methods for handling transitions and events, and a DSL will be provided for building them and for composing them.

This has a number of benefits:

• It's nicer to document. RDoc/YARD have much better support for documenting the methods of a DSL than for documenting the keys expected in a giant hash.
• It's more powerful. You can put arbitrary code in your callbacks.
• It catches typos better. Nonexistent DSL methods will error, while unexpected hash keys are simply ignored.
• It reduces the number of concepts involved. All of the different types of injections can more or less be rolled into one thing.

[sarahzrf]

Does the fact that this is part of the "GSoC 2016" milestone mean that I need to implement this in order to pass?

[sarahzrf]

I overhauled some stuff, and changed Designs in the process.