prep for v0.4.0.rc3

Update CHANGELOG.md

Update gemspec for release, new metadata (just-the-docs#911)

A couple of changes to prep for v0.4.0-rc1:

- bump the version
- add myself to the authors + email (this is primarily so that Patrick doesn't get siloed as the only maintainer; if you'd like to be added @just-the-docs/maintainers, let me know!)
- adds some more metadata ([gemspec docs](https://guides.rubygems.org/specification-reference/#metadata))
- updated the path to also include the CHANGELOG and favicon in the gem bundle

Merge pull request just-the-docs#455 from pmarsceill/v0.3.3

v0.3.3

Tweak search to make it less bulky

Update just-the-docs.gemspec

Merge pull request just-the-docs#369 from SgtSilvio/bugfix/css-main-s…

…earch-active

Fixed css .search-active.main

Merge pull request just-the-docs#327 from pmarsceill/dependabot/npm_a…

…nd_yarn/primer/css-14.4.0

Bump @primer/css from 14.3.0 to 14.4.0

Merge branch 'v0.2.9' of github.com:pmarsceill/just-the-docs into v0.2.9

Update package.json