Upgrade to clap 3.2

[epage]

I decided to use cargo-deny as a test case for upgrading to clap 3.2 which was just released (release announcement forthcoming).

For derive users, there isn't too much different. By specifying a default #[clap(action)] or #[clap(value_parser)] attribute, you opt-in to the new behavior that will be the default in clap 4.0. The main difference is instead of the parse attribute that is unique to the derive, you now have the value_parser attribute which comes from Arg::value_parser. When no value_parser is specified, we'll default to value_parser!(T) which will auto-select an appropriate value parser for the given field's core type. In practice, this means the default value_parser for PathBuf is now safe to use.

We also renamed ArgEnum to ValueEnum to make the name more meaningful and for some future work we'll be doing. value_parser mostly gets rid of the need for value_enum attribute except for when dealing with defaults, so I just left the attribute in place. I went ahead and switched some enums that were almost ValueEnum to being ValueEnum.

[Jake-Shadle]

Thanks!