Replace `&` with `&` in XML as `dee` doesn't seem to properly interpret `&`.

[bpoxy]

This fixes https://github.com/pcroland/deew/issues/44, see the issue report for more details and an example. This is a brute force / hacky solution and is definitely not ideal since, according to the XML spec, an unescaped & is not valid. However, dee doesn't properly handle the escaped version (&) so I'm not sure how else to solve this issue.