[css-snappoints] 11/6 Snap points draft update

Hi all,

I've addressed or added as issues to the snap points spec [1] the additional feedback from Rob's mail and TPAC.  Summary of the changes:

1. Added value "none" as default for scroll-snap-points-x/y
2. Mandated positive lengths only for repeat()
3. Added note to make more explicit that the animations and physics are intentionally left unspecified
4. Added issue for coming up with a way to specify a snap point at either end of scrollable content
5. Added issue to describe the guarantee that snap points make about scroll offsets as an invariant

Thanks!
-Matt

[1] http://dev.w3.org/csswg/css-snappoints/