Add 0.8.8 release notes

Author: xerial

RELEASE_NOTES.md

@@ -3,6 +3,8 @@
 ## 0.8.8
  * [Fix Unexpected UTF-8 encoder state](https://github.com/msgpack/msgpack-java/issues/371)
  * Make MessageUnpacker.hasNext extensible
+ * Added skipValue(n)
+ * [msgpack-jackson] Ignoring uknown propertiers when deserializing msgpack data in array format 
 
 ## 0.8.7
  * Fixed a problem when reading malformed UTF-8 characters in packString. This problem happens only if you are using an older version of Java (e.g., Java 6 or 7)