Fixed bug.

Adapted canonicity check for STCQ4 case was not completely correct and missed one situation.

See #2.
Removed some constraints for STCQ4 case.

See #2.
Alternate canonicity check for STCQ4.

In case of STCQ4 we can also interchange alpha with gamma while fixing alpha and delta. (This corresponds to switching b and c.)

See #2.
Added some extra documentation for STCQ4 case.

See #2.