Function: addhelp
Section: programming/specific
C-Name: addhelp
Prototype: vrs
Help: addhelp(sym,str): add/change help message for the symbol sym.
Doc: changes the help message for the symbol \kbd{sym}. The string \var{str}
 is expanded on the spot and stored as the online help for \kbd{sym}. It is
 recommended to document global variables and user functions in this way,
 although \kbd{gp} will not protest if you don't.

 You can attach a help text to an alias, but it will never be
 shown: aliases are expanded by the \kbd{?} help operator and we get the help
 of the symbol the alias points to. Nothing prevents you from modifying the
 help of built-in PARI functions. But if you do, we would like to hear why you
 needed it!

 Without \tet{addhelp}, the standard help for user functions consists of its
 name and definition.
 \bprog
 gp> f(x) = x^2;
 gp> ?f
 f =
   (x)->x^2

 @eprog\noindent Once addhelp is applied to $f$, the function code is no
 longer included. It can still be consulted by typing the function name:
 \bprog
 gp> addhelp(f, "Square")
 gp> ?f
 Square

 gp> f
 %2 = (x)->x^2
 @eprog
