no more seal
start of check implementation
pyret raco tools and check slightly borked
checkers ignored
Good checkpoint in `check` implementation, almost ready for merge
Testing for `check`

- Add test cases for what happens on errors...
  - During a check block
  - During a call to the check library
- Report check library exceptions and check block exceptions differently
- Clear out test results before running each program (may need to change if
  we extend to cross-module check blocks)
- Add a tester that allows us to inspect standard output
merge checks