Fixes #72 - Restructured arb int math and enabled BCMath as an engine

And this time shouldn't stall Travis CI
empty should only return true if `$x` is null, an empty string, or an empty array. empty() === isset() && !is_null()

Don't quote me on the isset() and is_null() they might need to give or take an underscore.

The only reason I bring this up is if you call `->input()` a fatal error will be thrown.