Add support for text/coffeescript+literate in the browser

The **sbp-literate** branch allows users of the browser-ready `extras/coffee-script.js` file to embed [Literate CoffeeScript](http://coffeescript.org/#literate) in web pages. For example:

```html
<script src="extras/coffee-script.js"></script>
<script type="text/coffeescript+literate">
This is a literate CoffeeScript example.

    console.log "Success!"
</script>
```

This results in "Success!" being displayed in the JavaScript console.

Contributors are urged by `CONTRIBUTING.md` to add their own tests. There are, however, no existing tests for the browser scripts functionality except for the test wrapper itself in `tests/test.html` For that reason, I have not added any new tests. I have of course tested that the code works on the web.

To build my local test, I ran:

    $ cake build
    $ cake build:browser

The results of that build do not form part of this pull request.