Con-splat-enate Arrays

[nonsensery]

What's this PR do?

Adds a section to the "Concatenating Arrays" chapter that uses the splat operator (...) in an array literal ([]) to concatenate arrays.

For example:

array1 = [1, 2, 3]
array2 = [4, 5, 6]
array3 = [array1..., array2...]

The Discussion section currently says that "CoffeeScript lacks a special syntax for joining arrays". I think you could argue that there is a special syntax for joining arrays, and this is it.

This pattern also has some nice features like:

• It's highly readable.
• It scales easily and clearly to multiple arrays. [array1..., array2..., array3...]
• It allows other non-array elements to be interspersed. [array1..., value1, value2, array2...]