Simple frame loom (cleaned up)

**Update:** I strongly recommend using [this loom](https://www.thingiverse.com/thing:7056512) instead, which is better in pretty much every way, and uses about the same amount of wood.

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This is more or less a direct copy of [Simple Frame Loom](https://www.thingiverse.com/thing:2274723/files) except significantly cleaned up. It also has three shuttles because why not? Multiple shuttles enable you to use different colors and make more complex designs, but if you only want one then just delete the other two.