Remove 'Maybe' wrapper around generated fields.

This may or may not be an improvement. I'm committing it because I want to
work on something else just now.
Add support for operator constructors.

Changed symbolic model checker to better match the paper it's based on.
Made LTL And and Or operators more symmetric.
Allow conversion of symbolic Integer to Int.

Also added some support for enabling debug in specific test cases.
Fixed another bug in symapp for integer.
Moved bounded model checker out of the smten repository.

And into the smten-apps repository.
Moved Sudoku out of smten repo into smten-apps repo.