Added formula for OpenAL Soft project

OpenAL Soft is a cross-platform software implementation of OpenAL that is useful for game developers who want a consistent cross-platform audio layer.

http://kcat.strangesoft.net/openal.html
Can a test be added to do something more substantial then e.g. `--version` or `--help`? See `cmake.rb` for an example of a formula with a good test. Thanks!