Fix trailing whitespace in Changelog
Deprecate setup_class in favor of load_class
Document MethodTemplate
Remove needless brackets
Rename #signal_definers to #ancestor_infos

This set of infos is not used to just find signals.
DRY up TypeBuilder code
Find parent builder directly
Rename method #parent to #parent_info
Use nested syntax to define GirFFI::GType
Remove outdated TODO
Extract logic to find things in ancestor infos
Describe ObjectBaseBuilder class
Move method builder setup into initializers