More granular reporting

[mattstevens]

Reporting changes to declarations as old and new values for the entire declaration is a convenient generic mechanism that applies to multiple modification types. However, it may be preferable to report distinct modifications for changes such as return and parameter types. This can simplify a report for situations such as the return type of many methods being changed from id to instancetype.

On the other hand, in some situations more granular reporting may be less convenient. For example, if a property's attributes are changed from strong to copy semantics the reader may wish to review the property's type even though it has not changed.