DOC: Add whatsnew for isnan and friends.
DOC: Add whatsnew for isnan and friends.

grundgruen/zipline,nborggren/zipline,bartosh/zipline,umuzungu/zipline,alphaBenj/zipline,florentchandelier/zipline,wilsonkichoi/zipline,grundgruen/zipline,enigmampc/catalyst,quantopian/zipline,magne-max/zipline-ja,Scapogo/zipline,humdings/zipline,wilsonkichoi/zipline,magne-max/zipline-ja,quantopian/zipline,bartosh/zipline,Scapogo/zipline,humdings/zipline,umuzungu/zipline,florentchandelier/zipline,nborggren/zipline,enigmampc/catalyst,alphaBenj/zipline