Dynamically create proto plus schema classes

[matthew29tang]

(Filing a feature request here as instructed by Anthonios)

I would like to use proto-plus to dynamically generate a proto plus schema.

Currently, a proto-plus schema class must have all its fields statically defined at the time of class definition (since the metaclass new method compiles all the fields). We would like to be able to create a schema with field names that are not known until runtime (retrieving field names from a variable). The dynamic creation should also work for nested protos as well.

[tonycombocurve]

Agree this would be a very useful feature.