This adds some new tools in CI for lint the book and also sets up
automated deployment to GitLab Pages. Also adds a readme that suggests
reading the book, since that's where all the information will be.
Without this, we're building a static rocksdb inside the rust-rocksdb
build script every time. As far as I know this doesn't change clippy's
behavior, but it does take a *long* time.
This drastically reduces the maintenance burden.
You may notice the `CODE_OF_CONDUCT.md` is deleted here. This is because
I don't feel like updating the relevant parts and I don't think this
will ever actually have a community build around it. If that changes for
some reason, I'm not opposed to adding a code of conduct again.
