Use "\samp{...}" instead of "``\code{...}''" when showing markup fragments

Use "\samp{...}" instead of "``\code{...}''" when showing markup fragments
in the running text.

For computed attribute and method names (where there's a \var{} part to
the name), use the non-indexing forms of \datadesc{} and \funcdesc{}.
This doesn't change the printed output, but removes 3 rejections from the
makeindex run and allows the LaTeX2HTML support to exclude these from the
index.