Create official mermaid-gitbook-plugin repo

[themightychris]

Hello,

I'm one of the many people maintaining a mermaid plugin fork for "legacy" gitbook

It's something I'm invested in keeping working, but it's depressing that we're all doing this in parallel

Could mine or any of the other forks get copied into the mermaidjs org? I'll volunteer as a maintainer and open issues in the other actively maintained forks to join. Then we could publish one authoritative and community-maintained version to NPM and stop having to do all this parallel work