#[postcard(crate = ...)] analogous to #[serde(crate = "...")]

[max-heller]

Analogous to #[serde(crate = "...")], it'd be great to have a #[postcard(crate = ...)] for #[derive(Schema)] to make it possible to re-export postcard derives from another crate without needing an additional direct dependency on postcard or postcard_schema.

This

postcard/source/postcard-derive/src/schema.rs

Lines 22 to 24 in 7011177

	impl #impl_generics ::postcard_schema::Schema for #name #ty_generics #where_clause {
	const SCHEMA: &'static ::postcard_schema::schema::NamedType = #ty;
	}

would have to become something like

impl #impl_generics #postcard::Schema for #name #ty_generics #where_clause {
    const SCHEMA: &'static #postcard::schema::NamedType = #ty;
}

Parsing could likely be handled similarly to #154, although it'd be nice to support #[postcard(crate = postcard)] instead of requiring a string literal like #[postcard(crate = "postcard")] (IIRC, the reason serde uses string literals is for backwards-compatibility).

[jamesmunns]

I'm open to a PR for this!