Make E2 error on division by zero

[Vurv78]

I see no reason for why users would want to keep a nan type, and it just leaves open potential exploits and whatnot as in c7cfcaa.

So I propose one of these things to happen on division by zero:

1. Throw a runtime error, regardless of @strict, on division by zero
2. Throw a runtime error on @strict, or return 0 without (gates do this)

Would need to deprecate isnan since it would never hold true.

[thegrb93]

Divide by 0 generates inf and 0/0 generates nan. You'd need to do this for every math function that can return error floats as well.