Modify `render_compound` to use kind rather than name for `objtype`.

This sets the CSS class of the emitted HTML element to the object kind
(e.g., `class` or `struct`) rather than the name of the object.

This change does not seem to affect the appearance of the generated pages
when using the Haiku theme, since it does not define rules for these
CSS classes in either case.
Display const/volatile qualifiers, "=0" for abstract methods, and "virtual" for virtual methods.