added execute command to main code
added execute command to main code

smharper/openmc,bhermanmit/cdash,liangjg/openmc,keadyk/openmc_mg_prepush,johnnyliu27/openmc,samuelshaner/openmc,paulromano/openmc,kellyrowland/openmc,wbinventor/openmc,amandalund/openmc,shenqicang/openmc,paulromano/openmc,paulromano/openmc,mit-crpg/openmc,mit-crpg/openmc,nhorelik/openmc,johnnyliu27/openmc,samuelshaner/openmc,shenqicang/openmc,mit-crpg/openmc,shikhar413/openmc,johnnyliu27/openmc,wbinventor/openmc,lilulu/openmc,johnnyliu27/openmc,mjlong/openmc,wbinventor/openmc,wbinventor/openmc,samuelshaner/openmc,keadyk/openmc_mg_prepush,shikhar413/openmc,lilulu/openmc,amandalund/openmc,kellyrowland/openmc,keadyk/openmc_mg_prepush,bhermanmit/openmc,liangjg/openmc,bhermanmit/openmc,walshjon/openmc,mjlong/openmc,nhorelik/openmc,lilulu/openmc,walshjon/openmc,amandalund/openmc,liangjg/openmc,smharper/openmc,smharper/openmc,smharper/openmc,paulromano/openmc,mit-crpg/openmc,sxds/opemmc,sxds/opemmc,shikhar413/openmc,liangjg/openmc,walshjon/openmc,walshjon/openmc,shikhar413/openmc,samuelshaner/openmc,amandalund/openmc