Re-added PR #80 for groups

[bozdoz]

I omitted changes to css and minified files, and added an example.

[afshinm]

Hmm, nice. The thing is, we can already pass a parent element and start the intro for a specific container rather than document.body.

Do you think these two have conflict with each other?

[bozdoz]

I think it would find the group matches within the selected element, wouldn't it? Don't think it would conflict.

[afshinm]

Do you think this PR can address an issue like this: https://stackoverflow.com/questions/46679734/intro-js-how-to-select-multiple-element-navigate-between-pages-with-continuous ?

[bozdoz]

That's quite an involved StackOverflow question, so I am not sure. My best guess use-case is to run one introjs after another, like in the example I posted with it: one iterated even numbered sections and the other iterated the odd, and there was a button for each.