Add in new functions for adding a list of servers at once to memcache.

new `addServers` function that is compatible with the php memcached extension.

new `addServersByStr` function that parses a string of the form: `127.0.0.1:11211,mc1.example.net:11211,mc2.example.net:11211`. This string is common in cloud environments for configuring memcache clients.