Update to work with 0.90.0

The current plugin version does not work with 0.90.0 because of missing classes. In addition the exception is swallowed in the MemcachedRestChannel class.

* Bumped the version
* The org.elasticsearch.common.Bytes class was removed from 0.90.0RC2 to 0.90.0, thus leading to compilation failure
* The Bytes class has been simply copied into org.elasticsearch.memcached.common in order to avoid conflicts