Prepare for v0.20.0 release

Since we have added new enum variants to the `StyleComponent` which was
not previously marked `#[non_exhaustive]`, we must bump left-most
non-zero version number (see
[specifying-dependencies](https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#specifying-dependencies-from-cratesio)).
Otherwise client code that do exhaustive matches on `StyleComponent`
will stop compiling.

Run `assets/create.sh`

doc/release-checklist.md: Clarify that you need to be fast

Also recommend to just push the tag for the release, and not all tags.

compiles and now se pass correct SyntaxSet too

Test deploy

Test deploy

Test deploy

test deploy

test deploy

test deploy