Release v0.2.91

[daxpedda]

Considering #3808 I would like to get the next release out soon.

Here is a list of things I believe would be nice to get in before the next release, but aren't necessarily a requirement:

• Shrink JS-allocated strings down to the correct size before passing them to Rust #3808 (actually required)
• Implement coverage output #3782
• Apply only allowed attributes to generated functions #3784
• Fixed temporary folder detection on MacOS #3817
• Deprecate --weak-refs in favor of run-time detection #3822
• Fixed nighly build of wasm-bindgen-futures #3827