Use methods instead of class instance variables. Fix delete_all issue.

This change uncovered a bug where the collection wasn't really being emptied on delete_all, but rather just being reset when done.
Create and save should always set updated_at. Add seconds to cast_to_date format
Add adapter for SQLite3, FMDB as dependency submodule, and sample app.
Model updates for SQL compatibility.

* resolved discrepancies with respect to using respond_to? rather than directly looking at provisioned columns
* method can a method that conflicts with an attribute reader method wins
* :belongs_to can accept an explicit :class or :class_name override
* virtual attributes can be assigned to @data, so that SQL SELECT statements work with more than just actual column names (i.e. for COUNT)
* more convenience methods a la rails
Poly wants a morphism