Calculates the hexadecimal equivalent of input.

1  –  Input

       A signed integer no larger than (2 ** 31) -1 (the maximum value
       that can be stored in a signed longword).

2  –  Output

       A hexadecimal character string.

3  –  Example

       DTR> PRINT FN$HEX(183)

        FN$HEX

             B7

       DTR>