Add new fully-accurate per-spark trace/eventlog events

Replaces the existing EVENT_RUN/STEAL_SPARK events with 7 new events
covering all stages of the spark lifcycle:
  create, dud, overflow, run, steal, fizzle, gc

The sampled spark events are still available. There are now two event
classes for sparks, the sampled and the fully accurate. They can be
enabled/disabled independently. By default +RTS -l includes the sampled
but not full detail spark events. Use +RTS -lf-p to enable the detailed
'f' and disable the sampled 'p' spark.

Includes work by Mikolaj <mikolaj.konarski@gmail.com>