Request: add support for case where multiple items visible #5

It is possible to use ViewPager to create a "carousel" effect, by having multiple items visible at the same time . This is typically done by setting e.g. ViewPager.setOffscreenPageLimit(3) and setting some appropriate margins.

In this mode, LoopingViewPager no longer works correctly at the transition between first and last items. This is because LoopViewPager has an internal fixed offset of 1 item, so if any more than one item is visible at once, these will not be shown correctly.

This can be fixed by allowing an arbitrary offset value to be set and changing the various hardcoded 1s to the new value, for example:

    public static int toRealPosition( int position, int count ){
        position = position-OFFSET;
        if( position < 0 ){
            position += count;
        }else{
            position = position%count;
        }
        return position;
    }

I have this working in my case, can send patch if interested.