tools lib traceevent: Man pages for get field value APIs

tools lib traceevent: Man pages for get field value APIs

Create man pages for libtraceevent APIs:

  tep_get_any_field_val(),
  tep_get_common_field_val(),
  tep_get_field_val(),
  tep_get_field_raw()

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/linux-trace-devel/20190503091119.23399-19-tstoyanov@vmware.com
Link: http://lkml.kernel.org/r/20190510200108.885426878@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>