skip route processing if another one is called

think:
page('/slow', function(ctx, next) {
    setTimeout(function(){next()}, 10000);
}, renderHtml);

page('/fast', renderHtml);

page('/slow');
page('/fast');

without this fix the html on the page would be from the slow route.
Merge pull request #172 from hugomrdias/feature/skip-callback-on-route-change

skip route processing if another one is called