[warning: this function is a bit out of date]
This function creates a list of gadgets, which can then be put in your
window by giving them as an argument to OpenW()(), or afterwards with
intuition functions like AddGlist().
buffer is mostly an ARRAY of at least GADGETSIZE bytes to hold all the
structures associated with one gadget, id is any number that may help you
remember which gadget was pressed when an Int()uiMessage arrives.
Flags are: 0=normal gadget, 1=boolean gadget, 3=boolean gadget that is
selected. Width is width in pixels, that should be large enough to hold
the string, which will be auto-centered. glist should be NIL for the first
gadget, and glistvar for all others, so E may link all gadgets.
The function returns a pointer to the next buffer (=buffer+GADGETSIZE).
Example for three gadgets:
DEF buf[MAXGADGETS]:ARRAY, next, wptr
next:=Gadget()(buf,NIL,1,0,10,20,80,'bla') /* the 1st gadget */
next:=Gadget()(next,buf,... ) /* any amount linked 2 1st */