errors: fixed bug in `VowsInternalError`
removed `pyvows.assertions`
`VowsAssertionError` → `AssertionError`
Replaced references to `expect` `decorators._assertion`, and `decorators._create_assertions` to preggy counterparts
tests.*: Updated test string checking to match updated preggy

The commit of “updated preggy” is:
 f7a9e617b9b842ee9f07641bd2f506c40fcc4469
reporting.common: better checking to format tracebacks
Updated requirements in project metadata

Updated in:

- Makefile
- REQUIREMENTS
- setup.py
- test_requirements.txt
- tox.ini
reporting.test: commented out problematic `except:` block