Rewrite from scratch the detection engine. Now it performs checks defined in payload.xml. User can specify its own.

All (hopefully) functionalities should still be working.
Added two switches, --level and --risk to specify which injection tests and boundaries to use.
The main advantage now is that sqlmap is able to identify initially which injection types are present so for instance if boolean-based blind is not supported, but error-based is, sqlmap will keep going and work!