Added test for toString according to HTML 5 draft
Added test for toString according to HTML 5 draft

shuizhongyueming/rangy,sashless/rangy,zimme/rangy,GerHobbelt/Rangy,djbuch/rangy,yangdm2015/vue-rangy,izhan/rangy,timdown/rangy,lpsBetty/rangy,sashless/rangy,brymacto/rangy,KamiHQ/rangy,lpsBetty/rangy,etodd/rangy,wotzisname/rangy,etodd/rangy,emil-mi/rangy,izhan/rangy,GerHobbelt/Rangy,brymacto/rangy,shuizhongyueming/rangy,zimme/rangy,wotzisname/rangy,timdown/rangy,djbuch/rangy,KamiHQ/rangy,emil-mi/rangy,yangdm2015/vue-rangy