Enumeration of types of list items available for listing entries.
Entries are ids in their binary form encoded as Base64 in JSON (and raw bytes in Smile).
Return type will be <link>StorableKey</link>
Entries are external textual representations of ids; Strings that can be converted
back to raw ids as necessary, but can also be printed out for diagnostics.
Return type will be
Object entries that include id (in binary form) as well as small set of
additional StoreMate-level metadata.
Accessor for getting
of actual items returned with this