units.1:
- Change the description to a more descriptive "conversion calculator".
- Sort options.
- Split the description into sections to make it easier to navigate the manual page.
- Improve the description of various options.
- Document the default value of the output format.
- Use more mdoc macros for better readability.
- Document the behavior of the PATH environmental variable.
- Improve examples.
- Add sections: EXIT STATUS, DIAGNOSTICS, and HISTORY.
- Document that units(1) cannot convert negative values and it handles long unit lists poorly.
units.c:
- Remove trailing whitespace.
- Sort longopts elements.
- Print usage instead of the path to the units file as documented when -V is specified.