rename .refresh() to .updateOffsets()

I kept putting "update offsets" as the comment next to .refresh(), and
that's just silly.
change alwaysRefresh to be more flexible, rename it
rename `one` to `unveil`

I guess jquery.unveil was onto something with that name. I had a hard
time looking up alternatives.
attempt to add grunt/qunit
add first test
add some elementary tests
fix .visible() should get the top target
add tests for the other target selection methods
Merge branch 'qunit'
add aboves and belows methods
add scroll event
fix offsets were stale in some events
change test LIs to base 36
add offset and bleed params to visibility tests
refactor to get active target from a lookup
change .active to . to support multple active targets
update lazy load image example to demo multiple elements
update npm test to run qunit
fix slice did not handle multiple elem at the same offset
refactor: cache offset locally