For example, if an arg is part of a required group, it will only appear
in the group usage string, and not in both the group as well as the arg
by itself.
Imagine a group containing two args, `arg1` and `--arg2`
OLD:
`myprog <arg1> <arg1|--arg2>`
NEW:
`myprog <arg1|--arg2>`
Closes#498
Tons of code has been moved into functions, deduplicated, made much
easier to read, maintain, and understand. Comments still need to be
added, but that will happen shortly. Modules have also been moved around
to follow Rust conventions and best practices.
All functionality remains exactly the same