Replace ExcludingMissingProperties with ExcludingMissingMembers
Cleanup ISelectionRule classes
Cleans up IMatchingRule hierarchy
Cleanup StructuralEqualityEquivalencyStep
Moves SelectedMemberInfo to its own type
Cleanup EquivalencyAssertionOptions
Cleanup IOrderingRule hierarchy
Cleanup ISubjectInfo
Adds and utlizes the 'ISelectedMemberInfo' interface rather than the 'SelectedMemberInfo' class.

I do not have a strong reason to do this, but it seems potentially more flexible in the future.
Removes GetIndexParameters from ISelectedMemberInfo