Issue #1 resolved
Drop key_prefix support
memcached clients have support for key_prefix: prepend key_prefix to each key in *_multi operation before sending keys to memcached server. This feature is redundant.
- the application must support keys with prefix and without prefix: for single and multi operation, e.g. in single operation prefix included into key, in multi passed as parameter.
- key_encode (this is useful to hash keys that are longer than 250 bytes (memcached limit)), because hash(key_prefix + key) != hash(key_prefix) + hash(key).
- separate key_encode function for key_prefix
- never apply key_encode to key_prefix