API : trace_handle

Add the trace_handle structure to allow the user to manipulate a trace.
Will be useful for getting information on specific trace files and
remove traces from a trace_collection without rebuilding the
trace_collection entirely.

Signed-off-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>