TO_STRING conversions

Conversions from different type to STRING.

Examples in ST:

str:=BOOL_TO_STRING(TRUE); (* Result is
'TRUE' *)

str :=TIME_TO_STRING(T#12ms); (* Result is 'T#12ms'
*)

str :=DATE_TO_STRING(D#2002-08-18); (* Result is
'D#2002-08-18' *)

str:=TOD_TO_STRING(TOD#14:01:05.123); (* Result is
'TOD#14:01:05.123' *)

str:=DT_TO_STRING(DT#1998-02-13-14:20); (* Result is
'DT#1998-02-13-14:20' *)

k := LREAL_TO_STRING(); (* Result is '1.4' *)