added support for OpenMP (though not thoroughly tested)
added support for OpenMP (though not thoroughly tested)

ekiwi/ligra,ekiwi/ligra,yunmingzhang17/ligra,yunmingzhang17/ligra,datachand/ligra,jshun/ligra,jshun/ligra,yunmingzhang17/ligra,deepsea-inria/ligra,datachand/ligra,deepsea-inria/ligra,deepsea-inria/ligra