TLAPM does not parse quantifiers using \forall or \exists keywords instead of \A or \E

[ahelwer]

Thanks to @muenchnerkindl for remembering this; opening an issue for tracking. This will fail at the syntax parse level:

---- MODULE Test ----
op == \forall x, y \in Nat, z \in Int, a, b, c \in Real : FALSE
op == \exists x, y \in Nat, a, b \in Int : TRUE
====

While this will succeed:

---- MODULE Test ----
op == \A x, y \in Nat, z \in Int, a, b, c \in Real : FALSE
op == \E x, y \in Nat, a, b \in Int : TRUE
====

Ref #159