GitLab

Closes: #2116

This restores commit 4ae029fc83bc38c4f79370c7bccaf38e30e342d6 from
git.xiph.org.

This restores commit f7c7db03f7cc00f75a273cbaa90321a5b68cb199 from
git.xiph.org.

Clean up/update homepage while here.

1.0.0 is a big release:
- 278 commits
- 174 files changed
- 12245 insertions(+)
- 11567 deletions(-)

This is restored commit ec2dacdd0414de36b48d1b90f40e2ffd0c7adc86 from
git.xiph.org.

Will be reapplied as applicable after restoring lost commits.

Build the static site on a continuous integration runner.
This provides both testing feedback on changes and simplifies
deployment.

Copied from the opus-website repository.

Just the plain copy of the docs from the repo for now, no
fancy markdown docs.

It was removed in newer jekyll versions.

Not available for linux, but only macOS and Windows