Turns a Base36 number into a decimal
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 Syntax

        GT_B36ToD(<cB36Num>) --> <nDec>

 Arguments:

      <cB36Num> is a character string representing a Base36 number
                This need to be in upper case.

 Returns:

      <nDec>    is a decimal integer

 Description:

      This function provides a method of unpacking numbers stored in
      Base36 format to decimal integers.  Base36 allows large numbers
      to be stored using very few bytes. Four bytes could hold a number
      as high as 1,679,615.  Useful for lookup table ID's.


 Examples:

      ? GT_B36ToD('ZZZZ')       // 1679615

      ? GT_B36ToD('11')         // 37

 Source: GTMATH07.PRG

 Author:  Philip Ide