[website] turn headers into hyperlinks

[akosyakov]

There are already hyperlinks in the specification:
https://microsoft.github.io/language-server-protocol/specification#textDocument_formatting

But it is not possible to copy them. I have to open the dev tool and copy it from there.

[dbaeumer]

Good idea. Anyone willing to do this 😃

[lewiscowper]

I'd love to take a look at this :)