top: extend command line sort field override provision

top: extend command line sort field override provision

In a effort to anticipate a potential future wishlist,
the recent '-o' sort override command line switch will
now support an override of the sort direction as well.

By prepending a '+' or '-' to any valid field name the
user will be able to guarantee a specific desired sort
direction. The '+' forces a high-to-low (normal) order
while a '-' reverses that to yield a low-to-high sort.

Without this addition users would be left to the mercy
of whatever was last specified for Curwin as reflected
in the rcfile or top's default of a high-to-low order.

(everything is perfectly justified plus right margins)
(are completely filled, but of course it must be luck)

Signed-off-by: Jim Warner <james.warner@comcast.net>