Revamp the OAI website to host multiple specifications along with OAS (e.g. Workflows, SLA, etc)

[frankkilcommins]

The exit process for new specifications coming out of Special Interest Groups require a home within the OpenAPIs website.

At a minimum, we need to:

• update the specs page - https://spec.openapis.org/
• create a pretty print version of the spec (via #42)

Optionally:

• Update the main website menu options / landing page to advertise multiple specs - https://www.openapis.org/