Get/set queue from Guile

[toothbrush]

This PR does a few things:

• Expose a queue:get-tracks and queue:set-tracks function to Guile land so you can.. well, you know.
• Implement an example using these new functions, shuffle tracks in queue.
• Make it build on my new computer. I really need to (one day..) make the XCode project auto-build dependencies instead of relying on flaky shit to find Homebrew-installed libs that really aren't intended to be used for building software against.

Kinda silly making a PR on my own project!