Add once.js

# once.js
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## About

Once.js is a 0.1kb micro-library that enables you to enforce a function can only be executed once. Once.js completely dependency-free and written in both CoffeeScript and JavaScript for AMD, Node.js and the Web.

## Examples

### JavaScript

```JavaScript
var canOnlyRunOnce = once(function() {
	console.log('That Happened!');
});
canOnlyRunOnce(); // 'That Happened!'
canOnlyRunOnce(); // *cricket cricket*
```

### CoffeeScript

```CoffeeScript
canOnlyRunOnce = once(->
  console.log 'That Happened!'
)
canOnlyRunOnce() # 'That Happened!'
canOnlyRunOnce() # *cricket cricket*
```


[build-url]: https://travis-ci.org/daniellmb/once.js
[build-image]: http://img.shields.io/travis/daniellmb/once.js.png

[gpa-url]: https://codeclimate.com/github/daniellmb/once.js
[gpa-image]: https://codeclimate.com/github/daniellmb/once.js.png

[coverage-url]: https://codeclimate.com/github/daniellmb/once.js/code?sort=covered_percent&sort_direction=desc
[coverage-image]: https://codeclimate.com/github/daniellmb/once.js/coverage.png

[depstat-url]: https://david-dm.org/daniellmb/once.js
[depstat-image]: https://david-dm.org/daniellmb/once.js/dev-status.png?theme=shields.io

[issues-url]: https://github.com/daniellmb/once.js/issues
[issues-image]: http://img.shields.io/github/issues/daniellmb/once.js.png

[bower-url]: http://bower.io/search/?q=once.js
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[downloads-url]: https://www.npmjs.org/package/once.js
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[npm-url]: https://www.npmjs.org/package/once.js
[npm-image]: https://badge.fury.io/js/once.js.png

[irc-url]: http://webchat.freenode.net/?channels=once.js
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[gitter-url]: https://gitter.im/daniellmb/once.js
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