See tests, the API is very basic
Returns a Q.Promise that resolves when the value is written to disk
Returns a Q.Promise that resolves to a Buffer
Returns a Q.Promise that resolves when the corresponding value is erased from the disk
Returns a Q.Promise that resolves to an array with values (Buffer) and/or nulls, depending on if values exist on disk or not
Deletes all stored values
Finish pending writes and die