Add support for bracketed html attributes

This is entirely a first pass, and I'm certainly a bit green on best practices with pegjs.  That said, I've run a number of tests, and within brackets, this should be a fairly flexible solution.  From what I can tell, the nature of the language and the terminators used make it somewhat difficult to add attributes without some sort of markup.  The bracketed markup aligns with slim conventions, (which @machty mentioned was a close relative):

http://rdoc.info/gems/slim#Attributes_wrapper

Everything's been tested, with a new test for this convention. I'm not sure why the build tools wrapped the method in a self executing function, I pretty much used existing build tools without modification.

Again totally open to feedback and I'll be happy to refactor accordingly.

I don't see the original `test "nesting"` case... only that you changed `test "nesting"` to remove the span, and we should keep the old test that tests with the span. Very specifically, the following test case should still be in the file, in addition to the altered span-less one:

```
test "nesting", ->
  emblem =
  """
  p class="hello" data-foo="gnarly"
    span Yes
  """
  shouldCompileTo emblem, '<p class="hello" data-foo="gnarly"><span>Yes</span></p>'
```