Three Dollar Quill

After a bunch of messing around, I've made some coverage improvements. At this point, the lack of coverage is localized to five files, and can be traced to three basic areas:

• Kind checks, which will require higher-kinded types to properly trigger.
• I haven't exercised a lot of the code I've written for universal types.
• I just don't have a good intuition for how to relate "how existential types are implemented" to "the stuff I find myself wanting to do with existential types", so I'm a little scared to touch them.

Hopefully, I can deal with the latter two soon. I may need to take a break from this project in the near future, but we'll see.

Good night.