Put TMG trelliscope into its own repo

[matt-dray]

Currently it's produced in the post and the output is saved to output/ of this blog to be served as rostrum.blog/output/goat_scope. This makes it hard to update. Split it into its own repo so it can be updated when TMG will (inevitably) release new material (they already have since this tool was made!).

• Code for getting the code with {spotifyr} is here: https://www.rostrum.blog/2019/04/25/gen-tmg-lyrics/
• Code for making the trelliscope is here: https://www.rostrum.blog/2019/06/20/goat-scope/