Improve error reporting
Improve error reporting on import.

This patch also does no longer try to deallocate a 
prepared statement after a failure. This didn't
work before anyways - but now execution stops
at the right time.
Bumps version number
Better code separation: adds Exec and PreparedQueries modules
Reenable SimpleCov
Improves error checking
Adds Metal#count shortcut
Adds some tests and documentation
Bumps version number