Fix #50: Handling of members access permission changes

Improved changed member detection to include those that were public/protected and are now package/private.
Added compatibility checks for access permissions (http://docs.oracle.com/javase/specs/jls/se7/html/jls-13.html#jls-13.4.7).
Fix for https://github.com/jeluard/semantic-versioning/issues/50
Can you detail this change?