Now Python host can force raw encoding for autoconverted .NET types.

What does this implement/fix? Explain your changes.

This class allows Python to override some automatic conversions done by Python.NET, which was otherwise impossible.

To do that, Python code can define a class derived from RawProxyEncoder, and override CanEncode to return True for the desired types. Create an instance of this class, and register it with Python.Runtime.PyObjectConversions.RegisterEncoder(instance) (see new test for example)

Does this close any currently open issues?

Enables workaround for #514

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Add yourself to AUTHORS
• Updated the CHANGELOG