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.
- Change behavior of -V to only print version and update the manual page accordingly. Previously, the program was printing its version and its units file. This didn't match the manual page, which said that the program would print its version and usage when -V is specified.