Closures presentation needs animations, syntax examples

[ybakos]

The Closures presentation is a bit weak and only illustrates the very basics of passing a block of code. This is because the presentation was derived from an older one about Objective-C blocks.

Improving the concept of passing closures could really benefit from some animation.

In addition, an animated progression from passing a function name, to a closure expression, to a closure expression without any type annotation, to using shorthand argument names ($0), to trailing closures would be very beneficial for students to see. The experience should be like whittling down from functions down to really terse trailing closure syntax.