perf stat: Introduce --control fd:ctl-fd[,ack-fd] options

Introduce --control fd:ctl-fd[,ack-fd] options to pass open file
descriptors numbers from command line. Extend perf-stat.txt file with
--control fd:ctl-fd[,ack-fd] options description. Document possible
usage model introduced by --control fd:ctl-fd[,ack-fd] options by
providing example bash shell script.

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/feabd5cf-0155-fb0a-4587-c71571f2d517@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>