Add stable releases

[kjarosh]

This PR adds "Stable Releases" section to downloads (if there are any) and replaces the default download links with the latest stable version (or the latest nightly if there's no stable). By default 3 last minor, and 2 last major releases are shown. "Compatibility" still uses nightly for measuring progress.

This PR may be tested by switching the repo in config to kjarosh/ruffle (there are some test releases).

[Dinnerbone]

LGTM

I wonder why it had a random reformat... do we not auto format in this repo? 🤔

[kjarosh]

Hmmm... Running prettier . --write gives me 14 more changed files, so I guess formatting code is only a suggestion in this repo 😄

[danielhjacobs]

Fun fact, back when we used Jekyll, we had a small setup for stable releases, but it was removed with the switch to React:

ruffle-rs.github.io/index.html

Lines 245 to 247 in 085ac08

	{% if full_release.size > 0 %}
	{% include releases.html releases=full_release limit=5 %}
	{% endif %}

[danielhjacobs]

That setup was "5 last stable releases", no separation of major/minor.

[kjarosh]

Fixed searching for stable releases. Currently we have to traverse all releases to find out there's no stable releases (which takes around 15s, 80 releases per page, ~15 pages).

Also changed maxMajor to 1 in order not to traverse all releases when we have only one major version.