refactor collection interface about bud HOT 2 OPEN

A couple todos here:

• at minimum, should insert private/protected appropriately on methods to clarify API
• better would be to refactor into separate modules for:
  • schema metaprogramming
  • semi-naive logic to manage the 4 collection partitions and enumerate properly
  • persistence of the partitions (mix-and-match would be nice)

from bud.

Would also be nice to move the semi-naive logic out of the collection interface proper -- i.e., the collection interface should provide the functionality that our semi-naive implementation requires, but shouldn't need to be concerned with the details of delta-driven evaluation itself. See also #54 and #57.

from bud.