Exposes an `overrideEmacs` which can take a package function that
receives the current package list and can make arbitrary modifications
to it.
This makes it possible for me to maintain a private overlay for e.g.
work purposes with packages that should not be visible in my public
repos.
This incredible package provides a fully functional, libvterm based
terminal emulator inside of Emacs.
Killer feature: It's possible to switch the buffer into a full Emacs
text mode (read-only) for selections and such.
Builds an Emacs that is not only configured with the required packages
but with the entire Emacs configuration for my personal setup.
This means that `nix-env -iA tools.emacs` will install a
fully-configured Emacs that can be launched as the window manager from
my ~/.xsession.
