Allow Boolean variables in guards and updates

[seblund]

Allow boolean variables in guards and updates such that:
Users can declare boolean variables and initial values in declarations:

bool a = false;

Users can use boolean variables in guards:

x < 2 && a == true && b == false && a != b

Maybe we should further allow x < 2 && a && !b (I think we should) but we can discuss that in this issue.

Users can update boolean variables in updates:

x=0, a=!b, b=true