Added code for supporting async
Added code for supporting async

Added code from this topuic https://github.com/troygoode/PagedList/issues/80#issuecomment-47106683.
Author - @iliakolesnikov
kpi-ua/X.PagedList,kpi-ua/X.PagedList,ernado-x/X.PagedList,ernado-x/X.PagedList,dncuug/X.PagedList