Upgrade the Migration Guide for 5.6

Author: Sanne

migration-guide.adoc

@@ -1,29 +1,21 @@
-= 5.5 Migration Guide
+= 5.6 Migration Guide
 :toc:
 
-This guide discusses migration from Hibernate ORM version 5.4 to version 5.5.  For migration from
-earlier versions, see any other pertinent migration guides as well.
-
-== Background
+This guide discusses migration from Hibernate ORM version 5.5 to version 5.5.
 
+For migration from other versions, see https://github.com/hibernate/hibernate-orm/wiki/Migration-Guides .
 
 == Known changes
 
-This version is very similar to Hibernate ORM 5.4; essentially it includes all bugfixes that have been
-applied to the 5.4 maintenance releases, and on top of this it introduces support for the Jakarta Persistence
-API (in addition the the JPA APIs we already support).
-
+This version is very similar to Hibernate ORM 5.5, with the exception of having removed some long standing deprecated features.
 
-=== Dom4J based XML mapping
+=== Javassist removed
 
-The implementation of Hibernate's parsing of XML mapping definitions has been entirely reimplemented based on
-JAXB rather than DOM4J, making progress to remove this ancient dependency.
-No specific issues are known at this time.
+It is no longer an option to choose Javassist as implementation used for the bytecode enhancement of entities.
+Byte Buddy has been the default for some time, and Javassist has been deprecated for some time and now has been removed.
 
-=== Removed the ability to disable "enhanced proxies"
+This should have no functional impact on applications; the only exception being that it's not longer valid to
+configure `hibernate.bytecode.provider=javassist`: remove the property if you're using this.
 
-The "enhanced proxies" feature has been introduced as a performance improving feature in 5.3 initially, at
-which time it was optional.
+A side effect is that Hibenate ORM no longer lists javassist among its dependencies.
 
-Since then, many more corner cases have been fixed and this feature is now always enabled. Enjoy the improvements!
-No changes are expected to be needed in user code to benefit from this.