Rename `failure_t` to `failure_reason_t`.
Add `location_t` with stringify function.
Add new `failure_t` struct with location information.
Adapt harness logic to keep track of location.
Add a test failure handler that reports assertion failures
on test setup and test teardown.
Most of them simply forward to the verbose handlers,
however, should we decide differently in the future,
existing unit tests will not have to be adapted.
Failures will not longjmp, but are reported on top of the stack,
by calling the case failure handler, which then decides whether to
continue or abort testing.
Other changes:
- Individual cases can have their own setup and teardown handlers,
- Case repeats are now handled by the case handler returning `control_flow_t`,
- Separates `status_t` and `failure_t`,
- Implements useful default case setup and teardown, and
- Keeps score of passes and failures on per case and test basis.