Consider mapping var to a specific role

[scottaohara]

Follow on to #373

Similar to #417 , it seemed reasonable to map var to role=code. If doing this, there would likely be some minor editorial to the ARIA spec for the role=code definition to account for the expanded scope beyond just being a role for the <code> element. There are other elements in HTML (e.g., <samp> or <data>) that may also fit this more general "code" category. Further discussion needed.