Set default-features = false on rkyv

[EmilioLaiso]

Using default features pulls in the size_32 feature, but the choice of the size_x feature should be left to the top-level crate as it was thought of in #223 (comment) and #223 (comment), and should be working now that glam-rs is on edition 2021 and rust >= 1.50.

[MarijnS95]

@bitshifter what's your preference to set these "required" features on dependent crates to have the least friction while developing glam? We've put it in [dev-dependencies] so that --all-features (as long as it is used with e.g. --all-targets), but that obviously isn't taken into account for cargo doc.

[bitshifter]

I suspect I left default features enabled on rkyv because I ran into this problem. Ideally default features would be disabled for all dependencies. I wonder if there is something rkyv could do to make this easier to deal with.

[MarijnS95]

@bitshifter Unfortunately I don't think cargo really allows for something better... except --cfg in RUSTFLAGS which can be controlled globally and don't require this mess as long as there's a sensible default somewhere.

[bitshifter]

I guess I can live with rkyv being a dev-dependency. Adding --features "rkyv/size_32" to the doc build should fix it I think, at least that worked locally.

[MarijnS95]

@bitshifter that works indeed. I'm not too keen on having it hardcoded there, but it seems to be the only solution 👌