Support for reaching top of the element.

- added "edge" parameter support (default to "bottom")
Minor cleanup
Minor changes

- preventing smack from setting more than one event listener for scroll
- fixed variable names
Tests
Merge remote-tracking branch 'origin/pr/5' into pr/5

Conflicts:
	src/jquery.bum-smack.js
Stubbed Tests
Skipping the threshold top edge tests
Comments for clarification. Moved the setting of data attribute to only when the smack options change
Rebuild WIP 1.2
Merge pull request #5 from pawel-piskorz/issue2

* Support for reaching top of the element (no threshold yet)
* Support for multiple edge bindings on the same element