Adding support for Amazon Elasticache

Takes advantage of Elasticache's auto-config mechanism: saves you from having to maintain the list of cache nodes in the client.  To use, add your elasticache configuration endpoint to your conf as elasticache.config.endpoint={config.endpoint}.  For example, elasticache.config.endpoint="mycachename.asdfjk.cfg.use1.cache.amazonaws.com:11211".