Accept nonpresent links

Currently, if the page is loaded with a hashlink for which the target element is present on the page but there is no link to it present, skrollr-menu will prevent the browser from scrolling to the element as it should, but not replicate the functionality. 
This commit will create a link to the correct element and then activate it if there is not already a link present. 
That would work, but would mean creating a `_dummyLink` on every init, regardless of whether it's needed. 

Since this function `jumpStraightToHash` is only run once at the end of initialization anyway, this method means that the dummy link is only created if needed and a maximum of once, since it's triggered on page load which, I think, is more efficient.