Operators enum

[bananu7]

This is a rather important change from the refactoring standpoint, but sees almost no improvement from the user's PoV. In fact, the operators aren't available as functions anymore, which requires using special code if one wants to use them as such.

For the VM, however, this means eliminating a lot of vmThrowErrors, which were there because the arity of operators wasn't guaranteed at callsite. Right now the parser call information is properly preserved right until the call.

This also required moving all the operator code to Eval.Eval. While this made the module grow significantly, I don't think it's such a huge issue in the end. Operators now being core parts of the language really don't belong in the outer modules, and it was just that much easier to implement them there.

There are still a few things left to polish, namely fixing the comparison parser test, fixing names for internal op impl functions and some other small changes.

[bananu7]

As for the issues closed, #5 and #40 obviously, #44, but also potentially #33, #42?