Feature/Rust: Use #[cfg()] in enum/foreign_enum

[kwek20]

Hi!

I would like to have a specific enum generated only when the rust config has a feature enabled as well.

Rust enum example:

pub enum ManagerStorage {
    /// Specialstorage.
    #[cfg(any(feature = "feature1", feature = "feature2"))]
    SPECIAL,
    /// Cool storage.
    #[cfg(feature = "feature3")]
    COOL,
    /// Regular storage.
    REGULAR
}

If I try to add these cfg options inside a foreign_enum macro, I receive the following error:
error: Expect doc attribute or doc comment or derive here, got 'cfg (any (feature = "feature1" , feature = "feature2"))'

If I leave out the cfg options, and compile without those features i get the following error: (Java example)
no variant or associated item named "COOL" found for enum "ManagerStorage" in the current scope
(Due to the actual enum beeing linked to something in the feature crate)

Is there a way to do this currently?

Thank you for developing this crate!