OpenAPI Support

[ZeroIntensity]

Improvement Description

OpenAPI has some features that can be quite useful for generating and using API's. It was not implemented before because I didn't want to. This will probably end up deprecating the current documentation generation API (which isn't public anyway), but the markdown content generation will likely stay the same.

Improvement Request Example API

from view import new_app

app = new_app()
app.spec()  # openapi specification

Anything else?

This will delay #74.