Minor hex lattice improvements for #331
Minor hex lattice improvements for #331

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