Feature request: Support bitflags #863
Description
The bitflags crate is really pervasive in Rust code.
It would be nice to be able to support #[derive(Facet)] inside bitflags! { ... } somehow, but if that isn't possible it might be necessary to introduce either a facet_bitflags! { ... } macro wrapper, or a FacetBitflags alternative derive macro. Are there other good options, short of actually patching bitflags to support facet?
Behavior: Bitflags are a bit like enums and a bit like sets. It would be important to support operations like contains(...) -> bool, intersects(...) -> bool, and union(...) -> Self in the vtable. Raw access to the bits would also be nice.
For serialization, I would expect bitflags to serialize as "list of enum variants" in high-level/human-readable formats and as the raw bitmask in low-level binary formats.