fix: dev: Removed `VowsAssertionError` and `_AssertionNotFoundError`

Should not have been here after merging the changes from refactoring for preggy.  Well, they’re gone _now_...
chg: dev: Comments in `cli:main()`
new: dev: Added tests/result_vows.py
chg: dev: "# pragma no cover"
chg: dev: @minor Use `cls` in `Vows.run`
chg: dev: @minor DRYed `Vows._get_first_available_topic()`
chg: dev: @minor utile: Use a list comprehension instead of `filter()` for `locate()`
chg: test: Added "pragma: no cover" to places where coverage is unlikely to help
fix: dev: Fixed typo from earlier commit in `core`