Trick for emptyInsertThreshold

[Yopai]

Hi,

The emptyInsertThreshold is not really needed (at least in recent browsers), as the function can be obtained by a pure css solution.

I propose this in the README - of course you're free to rewrite it and/or put it somewhere else.

Other ideas :

• Managing automatically an "empty" class when the list is empty (not relying on the :empty which works only if there's no node at all, even text ones)
• Have an "emptyPadding" option, adding automatically padding on an empty list. Note that the required padding can be bottom and/or right, or even top and/or left