Add a new feature "tracing" that enables tracing functionality via the
"tracer" crate (sadly features and crates cannot share the same name.)
Setup: tracer::start()
The main functionality is a tracer::trace_scope()! macro that will add
trace points for the duration of the scope. Tracing events are per
thread.
Finish: tracer::end() this will write the trace file (pretty printed
JSON) to a file in the current directory.
Signed-off-by: Rob Bradford <robert.bradford@intel.com>
