* Fixes memcached client expiration date issue

* Fixes memcached client expiration date issue
  Ref. Issue #96 (https://github.com/enyim/EnyimMemcached/issues/96)
* Updated StatusCodeEnum consistent with the Memcached protocol (and SASL auth extensions).
* Added code throughout to convert int status codes to the enum.  Added NodeNotFound and Unknown status codes, and return when a node cannot be located.
* Removed unused references.
## Note - Use of the methods that provide memcached feedback, their int results are now enums. This will require very minor code changes, but these changes will improve existing code readability and should be considered beneficial.