Feature/add gomemcache

Add optional golang based gomemcache library. 
This library does not require libmemcached, and provides it's own pooling, but does not offer the level of control that gomc does. This library has NOT yet been fully load tested.

@bbangert || @kitcambridge r?
We really should add a retry helper eventually...maybe wrap the `gomc`/`gomemcache` operations in a generic `MemcacheAdapter` (this would avoid a lot of the duplication, too) that defines `Get, Set, Delete` methods. Those functions could retry failed operations automatically.