Update README.md
Adding support for arbitrary constraints

Minor spelling correction

Adding custom constraint demo for both X and Y axis

Updating reference to document to window

Updating condition to nested if

Updating README.md and defaults comments to match

Updating constrainTo to accept array for handling arbitrary constraints
v0.4.6 - custom constraints
update support section of README
removed list to IE videos
more improvements to sortable-list-touchold demo
Merge branch 'master' into sortable_list_demo

Conflicts:
	dist/jquery.pep.min.js