tools lib traceevent: Man pages for libtraceevent event get APIs

Create man pages for libtraceevent APIs:

  tep_get_event(),
  tep_get_first_event(),
  tep_get_events_count()
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/20190503091119.23399-17-tstoyanov@vmware.com
Link: http://lkml.kernel.org/r/20190510200108.561088129@goodmis.orgSigned-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/Documentation/libtraceevent-event_get.txt

+libtraceevent(3)
+================
+
+NAME
+----
+tep_get_event, tep_get_first_event, tep_get_events_count - Access events.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <event-parse.h>*
+
+struct tep_event pass:[*]*tep_get_event*(struct tep_handle pass:[*]_tep_, int _index_);
+struct tep_event pass:[*]*tep_get_first_event*(struct tep_handle pass:[*]_tep_);
+int *tep_get_events_count*(struct tep_handle pass:[*]_tep_);
+--
+
+DESCRIPTION
+-----------
+The _tep_get_event()_ function returns a pointer to event at the given _index_.
+The _tep_ argument is trace event parser context, the _index_ is the index of
+the requested event.
+
+The _tep_get_first_event()_ function returns a pointer to the first event.
+As events are stored in an array, this function returns the pointer to the
+beginning of the array. The _tep_ argument is trace event parser context.
+
+The _tep_get_events_count()_ function returns the number of the events
+in the array. The _tep_ argument is trace event parser context.
+
+RETURN VALUE
+------------
+The _tep_get_event()_ returns a pointer to the event located at _index_.
+NULL is returned in case of error, in case there are no events or _index_ is
+out of range.
+
+The _tep_get_first_event()_ returns a pointer to the first event. NULL is
+returned in case of error, or in case there are no events.
+
+The _tep_get_events_count()_ returns the number of the events. 0 is
+returned in case of error, or in case there are no events.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <event-parse.h>
+...
+struct tep_handle *tep = tep_alloc();
+...
+int i,count = tep_get_events_count(tep);
+struct tep_event *event, *events = tep_get_first_event(tep);
+
+if (events == NULL) {
+	/* There are no events */
+} else {
+	for (i = 0; i < count; i++) {
+		event = (events+i);
+		/* process events[i] */
+	}
+
+	/* Get the last event */
+	event = tep_get_event(tep, count-1);
+}
+--
+
+FILES
+-----
+[verse]
+--
+*event-parse.h*
+	Header file to include in order to have access to the library APIs.
+*-ltraceevent*
+	Linker switch to add when building a program that uses the library.
+--
+
+SEE ALSO
+--------
+_libtraceevent(3)_, _trace-cmd(1)_
+
+AUTHOR
+------
+[verse]
+--
+*Steven Rostedt* <rostedt@goodmis.org>, author of *libtraceevent*.
+*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>, author of this man page.
+--
+REPORTING BUGS
+--------------
+Report bugs to  <linux-trace-devel@vger.kernel.org>
+
+LICENSE
+-------
+libtraceevent is Free Software licensed under the GNU LGPL 2.1
+
+RESOURCES
+---------
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git