Redesign variable bindings

[KacperFKorban]

Variable bindings should be redesigned. ATM our bindings work in a specific way and map any bound B on variable A to logical condition A =:= B. This is not enough.

The easiest solution would be to make it work in a similar way the compiler does this:
Remember the type of bound and for every variable have a low and high bound.

Things to consider before/during the implementation:

• Performance may be an issue since we have to evaluate more complicated checks.
• This problem is IMHO nontrivial. e.g. Case of a bound depending on another type variable.