ANSI Colors in Command Line Output

I always like it when command line programs offer colored output, which helps to discern between various stages of output, highlight errors and other important information. This is done with ANSI color codes, which are a somewhat archaic technique, but we can implement a nice wrapper to make it easy to work with in Swift.

This is a companion discussion topic for the original entry at https://nsscreencast.com/episodes/467-swift-command-line-ansi-colors