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?
Nit: for these shorter cases where err is already defined, it can be nice to cut down the LoC a little by putting it on one line:
```go
if err = json.Unmarshal(raw.Value, &result); err != nil {
    return nil, err
}
```