defface doc misses default and some more errors

["Lennart Borgman" <lennart.borgman.073@student.lu.se>]

The docstring for defface does not mention (default ...)

And I believe that

"DISPLAY can either be the symbol t, which will match all frames, or an
alist of the form ((REQ ITEM...)...).  For the DISPLAY to match a
FRAME, the REQ property of the frame must match one of the ITEM."

should be something like

"DISPLAY can either be the symbol t, which will match all frames, or an
alist of the form ((REQ ITEM...)...).  For the DISPLAY to match a
FRAME, the REQ property of the frame must match one of the ITEM for every
member of the alist."

I also am annoyed by the difficulty to get the possible values of
"window-system". If you look at the doc string for window-system (there is a
link in defface doc string) you just get the current value. In (defface
button ...) in button.el there is a (type pc). Is there such a value?
window-system for m "pc" is w32.