Add tests for some simple signals of Regress::TestObj
Avoid nil check
Move part of BaseArgumentBuilder#conversion_arguments to ITypeInfo
Inline #parameter_conversion_arguments
Refactor common output conversion for argument and return value builders
Stop using ITypeInfo#subtype_tag_or_class_name
Remove ITypeInfo#subtype_tag_or_class_name
Remove ITypeInfo#tag_or_class_name
Convert enums inside InOutPointer

- Make InOutPointer#set_value handle enum types
- No longer convert enums inside ArgumentBuilder
- Get rid of ArgumentBuilder#needs_ingoing_parameter_conversion?
Remove some single-use helper methods

This should clear up the dependency of argument builders on type info
somewhat.
Move BaseArgumentBuilder#argument_class_name to ITypeInfo
Add skip guard for Regress::TestObj's gtype property
Fix formatting
Add tests for Regress::TestStructA's fields
Add test for Regress::TestStructA.parse
Add tests for Regress::TestStructB's fields
Add test for Regress::TestStructE's some_type field
Make ITypeInfo#tag_or_class return :callback for callbacks

The callback objects currently do not have a nice printed
representation, so cannot be returned directly from this method.
Fix messed up search-and-replace
Convert enums inside InOutPointer#to_value