errors: make formatparse() an instance method on ParseError
It's just a little simpler this way.
Don't ask me what the "hg: " prefix signifies to the user, I just left
it as it was. I think we should consider changing the prefixes later
(maybe always use "abort: ", or maybe use more specific prefixes in
general).
Differential Revision: https://phab.mercurial-scm.org/D9347
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true