Add an interlace function

[charypar]

Works almost exactly like zip, except it can takes lists of different lengths:

interlace [1, 2, 3], ['a', 'b'] # => [1, 'a', 2, 'b', 3]

I'm not entirely sure about the order of arguments, it may make more sense to put shorter first, although I can't really see the curried form used much.