Offer migration to preservim org

[alerque]

Hey there!

This is a fantastic plugin that I've really enjoyed, and I know I'm not the only one. As as OSS maintainer myself I understand how time constraints go and priorities shift. Even with the best of intentions sometimes we don't have enough time to sink into projects we love. I've noticed this plugin has started to stagnate a bit and issues & PRs are not getting reviewed well. Several forks have cropped up with quite a but of support including multiple ones that merge the same PRs that have not gotten reviewed here.

I would like to offer a home for this on @preservim — an org home where we help popular plugins with ongoing community interest find extra maintainers. We've been maintaining nerdcommenter, nerdtree, tagbar, vim-markdown, and many others for years and all has gone pretty smoothly. You as the original author would retain ownership level access to the plugin, but I (and potentially others) would help monitor a team of contributors invited to pitch in with limited permissions. I would look through past PRs and current forks and find a couple high quality contributors and find a couple people interested in helping and invite them to a maintainer team. I would also lockdown the default branch to require at least 2 people (one contributor and one other signoff). I would then encourage those who have forked to pitch in and review existing PRs or submit their work back to the canonical repository.

This isn't a perfect model but it has worked has worked really well to revive and maintain quite a few plugins now and reversed the fragmentation across forks.

Because GitHub handles redirects for transferred repositories this is almost seamless for existing users.

[rollingmoai]

See #75 (comment)