New ids are prefixed with "_CPPv1". Replacing the prefix with "_Z"
should yield a valid mangled name following the Itanium C++ ABI,
except for expressions, which are currently not handled.
Elements now get multiple ids to keep permalinks permanent. The default
id is the newest style, which is used as the shown permalink and in the
index. The old style ids have been (partially) replicated and are
temporarily used as the default id for testing purposes.
