Adds support for the "%H" intro pattern without the need to install https://gitlab.mpi-sws.org/iris/string-ident.
I left the hook and make_string_ident_hook alone so that even the current version of https://gitlab.mpi-sws.org/iris/string-ident will work, but setting the hook doesn't do anything. Users can simply uninstall string-ident at their leisure, or use it with any older versions of Iris.
Fixes #404 (closed)