PDDL Case sensitivity

[RichardGubijev]

Subject of the issue

PDDL is not case sensitive, but the pddl library is.

Your environment

• Package Version [0.4.6]

Steps to reproduce

from pddl.core import Predicate
x = Predicate("case")
y = Predicate("CASE")
z = Predicate("CASE")
print(x == y) # False
print(y == z) # True

Expected behaviour

The library should not be case sensitive when comparing PDDL elements.

Actual behaviour

See code snippet above.

[haz]

Thanks, @RichardGubijev !

@francescofuggitti @marfvr I can take a pass at this -- just to confirm, we ok with leaving the casing as read, but ignoring casing just for comparisons?