Made Python API MultiGroupXS object xs_type attribute by_nuclide; nuclides paramter can now be all, sum or a list of nuclides
Made Python API MultiGroupXS object xs_type attribute by_nuclide; nuclides paramter can now be all, sum or a list of nuclides

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