jobstats: new library

jobstats: new library

This library provide API to measure time spend in particular parts of
code and to calculate optimal polling time.

To calculate a those statistics application code need to be divided into
parts (called jobs) that do something. It is up to application to decide
what is considered a job.

Series of jobs must be surrounded with the rte_jobstats_context_start()
and rte_jobstats_context_finish() calls. After that, jobs might be
started.  Each job must be surrounded with rte_jobstats_start() and
rte_jobstats_finish() calls.

After job finishes its execution, period in which it should be called
again is adjusted. It might be used to minimize time wasted on
unnecessary polls/calls. Adjustment is based on data provided by job
itself (ex: number of packets it processed).

After all jobs in serie are executed fallowing statistics are updated
and might be used by application. Statistics can be reset. Some of
provided statistic data:
 - total/min/max execution - time spent in executing jobs.
 - total/min/max management - time spent outside execution area. This
value might be used to measure overhead of scheduling jobs. This time
also contains overhead of rte_jobstats library itself.
 - number of loops that executed at least one job
 - executed jobs
 - time when statistics were reset.

Each job provide total/min/max execution time and execution count
statistics.

Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>