Macro enum_try_from

macro_rules! enum_try_from {
    (
        $(#[$meta:meta])* $vis:vis enum $name:ident {
            $($(#[$vmeta:meta])* $vname:ident $(= $val:expr)?,)*
        },
        $from:ident
    ) => { ... };
}

Defines the enum with TryFrom trait implementation.