Made nextStep and previousStep functions publicly accessible
Added missing commas
Add checkpoints to intro.js

Enable programmer to define which steps are checkpoints. I.e.
prevent the user from going back after certain steps. This is
useful if the user will be changing the state of the system
(creating a database entry, etc.) so the user doesn't go
back and redo their change.
Fix stacking context bug caused by opacity
Calling exit() on null issue solved
added onafterchange method, and call it just before the end of _showElement method

difference with onchange is that onchange is executed first time upon entering _showElement method. This will fail if we want to, for example, set focus to the current input element being shown, because the element is modified in _showElement method. onafterchange is executed just before the end of _showElement method, so any changes to the current element will persist. I found this especially useful when trying to set focus to an input element which is currently being intro-ed using jquery's .focus().
Do not add top marging if step numbers are hidden
Allow scolling to element to be set as option

* Auto-scrolling isn't always the user experience you want. Allow it to
 be turned off.
Added method _cloneObject

Added method _cloneObject makes a copy of the settings, that data is not overwritten.
change the loop condition
Merge pull request #226 from nanego/master

Only add top marging when step numbers are visible
Merge pull request #234 from eliovir/patch-1

Update index.html
Merge pull request #236 from adrianp/fix-229

fix issue with single-step pages (closes #229)
Merge pull request #227 from peterkinmond/master

Allow scolling to element to be set as option
Merge branch 'pasapsi-patch-1'
fix code style issues
Merge pull request #225 from andragan/master

added onafterchange handler, and call it just before the end of _showElem...
Merge branch 'master' of https://github.com/puneetkay/intro.js into puneetkay-master
fix coding style issue
Merge branch 'stacking-context' of https://github.com/dswen/intro.js into dswen-stacking-context