Kata

In many other programming languages (like Python, Java, etc.), there is a string.split() and a string.join() method.

The split method separates a string based off a separator provided (otherwise the delimiter is a space).

The join method brings together different values in an array, and the user provides what is in between the array values.

For any invalid inputs (like when str == nil or empty), simply return nil!

Now, create these methods for Lua!