Added surface normal functions.
Added surface normal functions.

smharper/openmc,shikhar413/openmc,johnnyliu27/openmc,smharper/openmc,mjlong/openmc,mit-crpg/openmc,shikhar413/openmc,shikhar413/openmc,liangjg/openmc,liangjg/openmc,bhermanmit/openmc,mit-crpg/openmc,walshjon/openmc,walshjon/openmc,amandalund/openmc,mit-crpg/openmc,wbinventor/openmc,smharper/openmc,kellyrowland/openmc,amandalund/openmc,walshjon/openmc,paulromano/openmc,shikhar413/openmc,samuelshaner/openmc,liangjg/openmc,wbinventor/openmc,paulromano/openmc,mit-crpg/openmc,walshjon/openmc,wbinventor/openmc,samuelshaner/openmc,johnnyliu27/openmc,amandalund/openmc,johnnyliu27/openmc,wbinventor/openmc,paulromano/openmc,amandalund/openmc,smharper/openmc,bhermanmit/openmc,paulromano/openmc,liangjg/openmc,samuelshaner/openmc,samuelshaner/openmc,mjlong/openmc,johnnyliu27/openmc,kellyrowland/openmc