[7.1] Migration Guide: Resteasy migration notes for 3.1.0.Final

Resteasy was upgraded in the EAP 7.1 to the new minor version 3.1.
It contains changes important for users and that should be documented.

Upstream documentation is available here: http://docs.jboss.org/resteasy/docs/3.1.0.Final/userguide/html/Migration_to_3_1.html