Update libgif.js
Update libgif.js

Update docs for new load_url function
paulvi/libgif-js,paulvi/libgif-js,ToadKing/libgif-js,sibnerian/sibgif,buzzfeed/libgif-js,buzzfeed/libgif-js,doclements/libgif-js,doclements/libgif-js,ToadKing/libgif-js