Update TODOs and FIXMEs
Remove unused argument builder methods
Avoid direct constant lookup in FunctionBuilder
Move CallbackReturnValueBuilder and CallbackArgumentBuilder to their own files
Flatten class hierarchy for CallbackReturnValueBuilder and CallbackArgumentBuilder
Extract local Convertor class from CallbackReturnValueBuilder
Move logic into Convertor
Extract Convertor class for CallbackArgumentBuilder
Extract Convertor class for ReturnValueBuilder
Use argument names when building callbacks, signals and vfuncs
Let callbacks and vfuncs store their own native versions

This ensures that the native versions are not garbage collected.
Always pass pointer to class setup functions

This avoids re-casting the object_class to a subclass.
Fix options for Yard to match moved files
Remove build status badge
Fix namespace for BaseArgumentBuilder
Fix formatting in documentation
Rename #post in Callback argument builder classes
Clarify public interface of CallbackArgumentBuilder
Clarify public interface of CallbackReturnValueBuilder
Move knowledge of need for conversion to ITypeInfo