aya/xtask
Dave Tucker 95e8c78db8 docs: Add labels for optional features
Following the lead of crates like tokio and nix, we now annotate APIs
that require optional features. This helps in cases where a user wants
to have an `AsyncPerfEventArray` which is documented on crates.io, but
it's not obvious that you have to enable the `async` feature.

Signed-off-by: Dave Tucker <dave@dtucker.co.uk>
..
src docs: Add labels for optional features
Cargo.toml aya-gen: Rename to aya-tool