Use CSS class names consistent with handwritten docs and display qualifiers on member functions.

The first commit modifies `render_compound` to make the CSS class names used consistent with those used by the C++ domain. (e.g., use `<dl class="class">...`, and not  `<dl class="std::vector<T>">...`).

The second commit adds `const`/`volatile`-qualifiers, the `virtual` keyword, and `=0` for pure virtual functions to C++ member function documentation.