- Move error formatting into a dedicated module
- Add a new 'minimal' output mode to describe how we show detail on a
  parse error -- and in theory, other well-known errors
  - Unlike the previous behavior, the 'minimal' format includes
    presentation of the `__cause__`

As a result, the output on a parse error will now include a one-line
presentation of the underlying error.

Ancillary things:

- Fix type annotations for the new interface: use `Literal`s
- Fix type annotations caused by `__cause__` handling (use
  `BaseException`)
- Fix some changelog formatting

resolves python-jsonschema#581