rename `_types` to be public

[samuelcolvin]

To something like schema_types, so types can be imported and used directly.

[ighmaZ]

Hi @samuelcolvin ! what should be done here?

[samuelcolvin]

The _types.py file needs to be renamed, and associated changes.

[ighmaZ]

@samuelcolvin so _types.py should be changed to schema_types.py everywhere . right?

[samuelcolvin]

Yes exactly.