Avoid TokenAware failure when keyspace not set

PYTHON-181; fixes KeyError when routing_key set with no keyspace
Make keyspace settable on all statement types

Change Statement.keyspace to be handled more like routing_key:
- now settable on simplestatements
- now set implicitly along with routing key in batch statements

Also:
- changed BoundStatement.bind to raise if not enough parameters for routing key
- fixed minor typo in example in comments
Set PreparedStatement.values in init

peer review input
Stop using strange dict(dict) for routing key test.
Merge pull request #225 from datastax/PYTHON-181

PYTHON-181 - Make TokenAware tolerant of queries with no keyspace set