First pass generalization of analytic initialization.  Still have to (a) allow custom analytics, and (b) fix tests to delete their temporary files.
Cleanup after new dataset tests, and standardize how we do so between live tiling and dataset tests.
Allow custom data and tile analytics to be specified in the .bd file
Make sure to add accumulators when doing live tiling.
Change accumulator infos from a list to a map to allow for multiple attempts to add the same accumulator - it just keeps one.
Make sure composite analytics forward accumulator requests properly.
Fix a bunch of comments in the analytics file, and add a bunch more needed ones.
Propagate analytic changes to twitter demo
Propagate new requirements for analytic initialization into graph and time-range binner classes.
Add an empty value and a minimum count for mean analytic.  Make min and max analytics handle NaNs.
Better documentation of analytic classes and the generic types therein
Merge branch 'analytics' of github.com:nkronenfeld/aperture-tiles into analytics
Merge pull request #28 from nkronenfeld/analytics

Analytics