Deprecated Code List
Backward incompatible changes
Thankfully, the list is not as extensive as it was from 5.2 to 5.3. It's even less than it was for 5.3 going to 5.4 or going to 5.5, so I think this will be easily adapted.
5.6 is still under development, but has reached a feature freeze state. So I do not expect any more changes in the upcoming beta, except for bug fixes only.