Moved event buffer initialization to simulation initialization function, rather than allocating and free'ing each power iteration. Also added ifdef for enabling/disabling event-based simulation.
Moved event buffer initialization to simulation initialization function, rather than allocating and free'ing each power iteration. Also added ifdef for enabling/disabling event-based simulation.

walshjon/openmc,mit-crpg/openmc,walshjon/openmc,shikhar413/openmc,liangjg/openmc,liangjg/openmc,walshjon/openmc,shikhar413/openmc,amandalund/openmc,paulromano/openmc,paulromano/openmc,paulromano/openmc,smharper/openmc,mit-crpg/openmc,amandalund/openmc,paulromano/openmc,smharper/openmc,smharper/openmc,shikhar413/openmc,walshjon/openmc,mit-crpg/openmc,liangjg/openmc,shikhar413/openmc,mit-crpg/openmc,amandalund/openmc,smharper/openmc,amandalund/openmc,liangjg/openmc