Sqlwhat

- Add optional `force_diagnose` parameter to `test_exercise` to force passing the `diagnose` tests in `check_correct`.

- Update ANTLR dependencies

Improved

- `has_error()` renamed to `has_no_error()` for more intuitive reasoning.

Added

- Function `check_query()` to execute arbitrary queries against the database to verify whether database state updates happened correctly.

Improved

- CI now runs all tests, including the ones that need the (private) `sqlbackend`.

**Contains breaking changes!**

- All functions that start with `test_` have been deprecated.
- `check_error()` renamed to `has_error()`
- New functions `has_nrows()`, `has_ncols()`, `check_row`, `check_column`, `check_all_columns`, `has_equal_value`
- piece-wise messaging (uses new functionality in protowhat)
- Complete rewrite of documentation, explaining both the result-based checks and AST-based checks
- Improve coverage to 99% by adding tests on both functionality (pass/fail) and messaging.
- Improve package structure and test structure in general