Remove deprecated wax tags

This merge request removes three tags: Reference header, Appendix header, and Reference.

For Reference header and Appendix header, any header (H1–H6) at the start of the section will function as a header for the section. The two tags were h1.referencehead and h1.appendixhead; now we don't pay attention to the class when parsing.

Reference has been replaced by any <p> or <li> in the Reference list. Those now get a § at the start to show that they're functionally references; their content is parsed as a mixed citation. Reference thus is no longer needed.