Alkali

* updated docs and comments
* test coverage back up to 100%
* Query copies manager objects at creation time, less effiecient but
less error prone
* implemented Query.distinct
* implemented Query.annotate

* implemented Query.aggregate functions: Sum, Count, Min, Max
* can access Field object via shortcut model.fieldname_field
* Fields are now descriptors on Model instance
* models now cascade delete when ForeignKey instance is deleted
* some minor speed ups

* no longer using IField as a zope interface, just have a Field class now
* IntField now has auto_increment property
* general work on ForeignKey fields, still not happy with implementation
* ForeignKey validation during save/load
* Fields now have more properties, links to model and meta class parents
* refactoring around how Model instances are created
* Query returns copies of Model instances
* Query speeds and Manager.get() are now faster
* general refactorings

* fix: model instances going to/from its manager are copied. this
prevents changing the saved version without calling save().
* added ForeignKey field
* memoizing Model.pk property
* don't allow changing of pk field once set
* added signals on model creation/deleting/saving/etc
* removed `.name` property from several classes
* minor speedups after profiling
* fix: during load/save a multiple table db would reuse the same storage class
* several documentation cleanups

Initial commit. Starting at v0.5 since alkali can accomplish some real work.