@UNQREADF[[u,]filename, "key", outputname, length] : Read a value from an existing key in a UnQLite database and save it to a file.
|u||Optional flag that the key is Unicode (UTF16)|
|filename||Database opened with @UNQOPEN|
|key||Key to read|
|outputname||Output file that will contain the value|
Returns 0 if successful, or an error if not.