top: add the field 'USED' to top's existing repertoire

top: add the field 'USED' to top's existing repertoire

After revisiting the issue of a new field, combining 2
existing fields (RES and SWAP), I've decided it indeed
makes sense. After all, with the vastly expanded field
capability and the ease of adding new fields, it would
save some precious horizontal screen real estate while
also eliminating some mental/manual user calculations.

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

Reference(s):
http://www.freelists.org/post/procps/top-enhancements-i-hope
http://www.freelists.org/post/procps/top-regression-reports

Signed-off-by: Jim Warner <james.warner@comcast.net>
 top/top.1     |   23 ++++++++++++++---------
 top/top.c     |   14 ++++++++++++--
 top/top.h     |    6 ++++++
 top/top_nls.c |    3 +++
 4 files changed, 35 insertions(+), 11 deletions(-)