merge turnstile-core and related branches into master

[stchang]

Opening this, but dont merge. Ready to merge!

• [x] I want to redo the merges more cleanly tomorrow.
• [x] And want to make sure travis tests pass

This pr combines:

• wilbowma/cur turnstile-core
• stchang/cur metantac
• stchang/cur generic-type-methods
• fixes from stchang/cur popl2020-artifact

So this includes all the additional work from your turnstile-core, as well as everything from popl2020-artifact except define-z3-axiom (to avoid dependency on rosette).

The tests should now pass with macrotypes master so after this merge, users should use cur master along with macrotypes master

[stchang]

Ready to merge!

[stchang]

I decided to leave all the commits bc I realized the fine-grained history is useful. I already did a lot of squashing while developing.

[wilbowma]

Okay! I'll press the big red (green) button!

[stchang]

fingers crossed

[wilbowma]

Okay merged! Does this work with macrotypes/turnstile master now?

[stchang]

yup. woohoo!

[wilbowma]

Huzzah! Thanks for all the work!