Procedural macro derive that mimics arg_enum! from clap

Usage

In Cargo.toml:

[dependencies]
arg_enum_proc_macro = "0.1"

In the rust code:

use arg_enum_proc_macro::ArgEnum;

/// All the possible states of Foo
#[derive(ArgEnum)]
pub enum Foo {
    /// Initial state
    Unk,
    /// Foo is on
    On,
    /// Foo is off
    Off,
}