Added a new option 'startitem'

- this will be used to select which item to begin with.
Set startitem - 1 as 'si'

- this is so that the value passed in as start item coincides with
  actual index
Set starting index to be 'si'

- Also corrected type in comment
Set 'left' position on ul using 'si' so the correct item is in place.
Set 'box-size' of list item to 'border-box'

- Done so that a padding can be set on each item without changing the width
  of the element.