Generate docs from schema files and store them in this repository

[neilmb]

This addresses #71

We generate Markdown format documentation directly from the JSON schema files and store the documentation here in the same repository. To make better and more readable documentation, this adds more title attributes in the schema.

[neilmb]

Generated markdown docs can be seen in https://github.com/GSA/dcat-us/tree/nmb/generate-docs/jsonschema/docs

[jbrown-xentity]

This documentation provides accurate representation of the schema. There is more iterative work to do in the future related to styling, simplification, etc, but this should be good as-is.