Provide memcached as an alternative to redis

[ispyhumanfly]

They're both the leading in memory data storage platforms. AWS and its ElastiCache provide managed services for them. Redis generally seems to win because of how much you can do with it, but memcached is being to be more simple, and slightly faster. We should offer this as an alternative.

[ispyhumanfly]

After discussions with @Logikgate we decided we should do this. As Avian moves to become a key agent in what is the "FlyPaper Application Stack" (lame name for now but it'll do), we want people to be able to take full advantage of the managed in memory caching systems available today. In AWS, Redis and Memcached are their main players. So we should support them.