tools lib traceevent: Man page for header_page APIs

tools lib traceevent: Man page for header_page APIs

Create a man page for libtraceevent APIs:

  tep_get_header_page_size(),
  tep_get_header_timestamp_size(),
  tep_is_old_format()

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/20190503091119.23399-5-tstoyanov@vmware.com
Link: http://lkml.kernel.org/r/20190510200106.583928896@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>