New feature/option to use introjs

Here I try to explain my case.  I was using `intro.js` as is (v0.6). And I encountered a bug (at lease it was bug for me). I introduce modal dialog to user. Inside the dialog I have some buttons (e.g. close dialog). So during intro user may press these buttons. And its bad, because he may close dialog and then examining area will disappear. But `intro.js` won't know about that the examining area disappeared and will continue an introduction.

P.S.  Examining area - a current area which are highlighted by `intro.js`  
![introjs1](https://cloud.githubusercontent.com/assets/1126672/2591435/5bd22862-ba6b-11e3-8c28-9748bd77f188.png)

There are also exists other cases where can be useful to disable an interaction with examining area/element (so user won't be able to press buttons or do anything else).

So what I did?
I decided to add this as option to `intro.js`. I added new option - `disableInteraction` (default value is `false`). And now developers can disable/enable interaction with examining area/element.

What do you think about it? 
Let me know!