Test escaping for attributes

[davepagurek]

We need to make sure that:

h1 Test (
  class "something_with_a_quote_\""
)

should become:

<h1 class="something_with_a_quote_&quot;">Test</h1>

...but, here's the weird thing. If we're doing a code block:

button Click me (
  onClick =>
    alert("hello");
)

that should actually become:

<button onClick="alert(&quot;hello&quot;)">Click me</button>

I didn't think that was valid but thats actually what is supposed to be done, it turns out, so we SHOULDN'T be using ~> for script attributes (script tags are another story.)

I think it's still a good idea to keep ~> in case you want to inline some html instead of emerald, but we should discourage using it for script attributes. We also need to investigate if any special escaping has to be done for script tag contents or if we an still use => there.