Added a modal background option, and an expose feature

to expose elements on the tour
also added postRide, postStep, and postExpose callbacks

Change-Id: I5717903e8b040388ad3400271c7c71e49bd89c46
Merge pull request #72 from ehudokai/master

Adding modal background option, and an expose element feature
Merge branch 'master' of https://github.com/zurb/joyride

Conflicts:
	joyride-2.0.3.css