Replaced F94 with F12

Minor revision to text of SYNONYM
Minor revision to rational for CS-PICK, N>R
Significatn revision to rational for FORGET
Added word numbers for N>R, NR>, SYNONYM, [DEFINED], [UNDEFINED]
Added implementation of [IF] [ELSE] and [THEN] taken from rationale of [THEN]
Removed implementation from rationale of [THEN]