Add `is_int` and `is_float` built-in methods

[johneastman]

Add methods for checking if a number is an integer or a float. It will return the result of Number.is_whole_number.

Number of arguments: 1 Accepted types: Number

One method can be used for both built-in functions.

[johneastman]

Instead of two separate methods, create one called is_whole_number.

[johneastman]

Commit: https://github.com/johneastman/boomerang/commit/1ff05a66fcf2435c60869bf9cfe6d80bcd403146