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?
It just occurred to me that these could be fetched in parallel, assuming `gomemcache`'s `.GetMulti()` doesn't do the trick (I remember you left a comment that `gomc`'s implementation was broken). Probably territory for a future pull request either way, though.