Support registering a multipole library to cross_sections.xml
Support registering a multipole library to cross_sections.xml

paulromano/openmc,smharper/openmc,amandalund/openmc,johnnyliu27/openmc,smharper/openmc,paulromano/openmc,johnnyliu27/openmc,amandalund/openmc,shikhar413/openmc,mit-crpg/openmc,wbinventor/openmc,johnnyliu27/openmc,liangjg/openmc,smharper/openmc,liangjg/openmc,mit-crpg/openmc,wbinventor/openmc,amandalund/openmc,mit-crpg/openmc,amandalund/openmc,paulromano/openmc,shikhar413/openmc,paulromano/openmc,walshjon/openmc,walshjon/openmc,mit-crpg/openmc,walshjon/openmc,wbinventor/openmc,shikhar413/openmc,smharper/openmc,liangjg/openmc,shikhar413/openmc,walshjon/openmc,liangjg/openmc,johnnyliu27/openmc,wbinventor/openmc