tools lib traceevent, perf tools: Move struct tep_handler definition in a local header file

As traceevent is going to be transferred into a proper library,
its local data should be protected from the library users.
This patch encapsulates struct tep_handler into a local header,
not visible outside of the library. It implements also a bunch
of new APIs, which library users can use to access tep_handler members.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux trace devel <linux-trace-devel@vger.kernel.org>
Cc: tzvetomir stoyanov <tstoyanov@vmware.com>
Link: http://lkml.kernel.org/r/20181005122225.522155df@gandalf.local.home


Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>