kill: add pretty printed list output (for compatibility with procps)

 * add -L, --table

References: http://www.freelists.org/post/procps/kill1-consolidation
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Karel Zak <kzak@redhat.com>
kill: support --list=<signal>

The '=' is expected for optional arguments and required in procps version.

Signed-off-by: Karel Zak <kzak@redhat.com>