Implement Index of system function

[GoogleCodeExporter]

See more here: http://www.aplusdev.org/APlusRefV2_14.html#106

Example:

Inventory :=    (("Oxford"; "Oxford";"Loafer";"Loafer");
         ("Brown";  "Tan";   "Black"; "Brown");
         (128.98;   175.98;  112.50;  112.50))


index := Inventory[0 1] _index_of (<"Oxford";<"Tan")

index pick 2 pick Inventory

Result:

175.98

Original issue reported on code.google.com by batori.c...@gmail.com on 6 Jun 2011 at 1:59