I expect we will also have the option to install the .whl files created
by wheel into a virtualenv, which seems like a good idea since they are
likely to be different versions from those installed on the target
system, if any.
I need to research exactly how to do that, maybe in a separate package
which is a dependency of the Booktype package. It would then be easy to
switch to distro-provided dependencies once Booktype supports them,
without having to change the packaging much.