Adding an Entity node type.
Add a way to define an error handler when executing sql.
Pass the `require_commit` param as well
Allow ``sql_error_handler`` to return a value.
Py3k fix, fixes #224
Allow custom options in meta
Small cleanups to the way the pk is determined.
wrong MySQLDatabase field override key for bool
Merge pull request #227 from spenthil/patch-3

wrong MySQLDatabase field override key for bool
Allow manually setting PK regardless of auto_increment, refs #226
Moving out of loop
Starting work on implementing basic composite key support
Building basic functionality for Composite primary keys to work.
Export CompositeKey and implement it as a descriptor.
Tests for CompositeKey.
Small nit that bothered me
Sqlite pk autoincrement, fixes #147
Adding test for custom option inheritance.
Removing todo item
Adding `case` helper, fixes #233