pidstat: Add scheduling priority and policy information

Display task scheduling priority and policy along with task switching
activity (-w option).

Signed-off-by: Cedric Marie <cedric.marie@openmailbox.org>
Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>
pidstat: Update manual page

Update pidstat manual page to document the new fields displayed with
option -w.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>