This adds new helper methods to the query result classes:
 - error_message
 - error_number
 - insert_id
 - query

All these provide new information on the query that was run.
In 0.1 we had those methods in the connection class. They are now in the result classes because the low level information we get is bound to the last executed query.
This means in 0.1 if you executed more than one query, you couldn't get information about the first one anymore after issuing a second. In 0.2 this is now possible since we
store this information directly after running the query (or fetching the result from the connection).

This requires http://reviews.lunr.nl/r/61/

Unit Tests