Refactoring in Progress. Massive Code Churn.

- Added __.flatten(array, shallowFlag). Not perfectly
  performant, but definitely readable.

- Added __.get(obj, key) to complement __.has(obj, key).

- Added BBM.isNode(obj) for checking if the object is
  a node object.

- Mostly finished with pruneList.js, and decided that the
  initial parse tree will need two small filtering steps
  before being available for consumption.

- Should probably just settle on a single BBM.fn.mapChild
  for iteration. Other children iteration methods can
  currently be emulated using this.children().forEach(),
  for example.

- Start filling in TODO placeholders with real names.