Fixing bool(), MRO and License

I didn't get the wa MAX(id) is faster than COUNT(*) if it needs to run and compare all values from the DB.
In the other hand I also fixes the MRO (it didn't complain in 2.X not sure why) and I added a license.

As far as I know many companies prefer to have a well known open source license which lets them work than just "public domain" which falls in a grey area which many lawyers do not recommend.