Improve CoverageJSON Ecosystem 1: Python Validator

[chris-little]

1. To improve the CoverageJSON ecosystem, a python validation tool to validate values and aspects that the JSON Schema cannot would be useful.

(In the longer term, if CoverageJSON becomes a full OGC Standard, the validator would be written in Java.)

[jonblower]

This comment is a note-to-self to define the requirements for this, with a view to defining a project. Could include requirements for validation and conversion between xarray, pandas, etc.

Would need to build on existing work with the schema.