Rebrand look & feel of the Marten documentation

[oskardudycz]

Make it more aligned with the current standards. Create proper landing page.

I like personally the look of Hasura web page: https://hasura.io/ and https://docs.hasura.io/1.0/graphql/manual/remote-schemas/index.html.

[mysticmind]

We are using VitePress for building the new v4 docs site. Currently VitePress does not yet support importing code snippets with named region like what is available in VuePress. I have sent a PR vuejs/vitepress#238 for the same.

In the interim, I will migrate the changes to use VuePress. That said, VitePress is blazing fast and would definitely I love to use it more.

Once the PR is merged and a new release is available, will migrate it back to VitePress.

[mysticmind]

We now have the VitePress based docs including handling of code snippets fully functional. Closing this.