new checkbox style

![screen shot 2014-08-12 at 21 54 38](https://cloud.githubusercontent.com/assets/170270/3896924/e8ff15a2-225c-11e4-8c58-a3bfe93a2176.png) ![screen shot 2014-08-12 at 22 10 21](https://cloud.githubusercontent.com/assets/170270/3896925/e9077b0c-225c-11e4-80df-e9d9b22c8f26.png)

*OS X left and Windows right*

I think these characters are much clearer. Also switched to using the [`figures`](https://github.com/sindresorhus/figures) module.

*(I spent 2 hours today going through the Unicode character table to find this one. lol)*


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For reference, the current one is:

![screen shot 2014-08-12 at 22 18 19](https://cloud.githubusercontent.com/assets/170270/3897015/e12caee2-225d-11e4-8137-784c994b31d6.png)


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Alternatively

![screen shot 2014-08-12 at 21 54 24](https://cloud.githubusercontent.com/assets/170270/3896932/15d20e04-225d-11e4-8943-326af63a6099.png)

But I think that's more of a radio button. Maybe you should have a `radio` prompt type?

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@addyosmani @passy @stephenplusplus @eddiemonge @silvenon

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closes #72