Adds support for Module abstracts and metadata

- Adds a `<div class="abstract">...</div>` to the body of the module as the 2nd child (after the title)
- Adds a separate XSLT file that converts module metadata to `<meta>` tags in the `<head>`, using ones defined in http://dev.w3.org/html5/spec-preview/the-meta-element.html when possible