To-do list
----------

- Formatting:
  - Consider implementing __format__ on the intermediate representation.
  - Make precision optional
  - Alignment and field width
  - Support for 'e', 'g', '%', 'n'
  - Support for thousands separators
  - Find a way to resolve ambiguity between the two uses of z (for round-ties-to-zero
    and for negative sign suppression). We also need to resolve
    ambiguity between 'e' for "even" and 'e' for the type.
    Suggest prefix of "r" for specifying rounding mode.
  - Support for form of scientific notation with zero digits before the point:
    3.1415 -> .3142e-1
  - Make number of digits and the presence of a + sign in the exponent adjustable.

Done
----

- Add __all__ to __init__.py
- General maintenance
  - Add actions workflows
- Convert namedtuple types to typing.NamedTuple subclasses, or perhaps dataclasses.
- Implement round_05away
- Add isort config
- Formatting:
  - Sign management
- General maintenance
  - Add package structure: setup.py, etc.
  - Remove setup.py in favour of pyproject.toml
