Package intermodal for Debian

It would be nice to get intermodal into the debian package repository, where it will also be picked up automatically by distros like Ubuntu.

For [just](https://github.com/casey/just), I've relied on users to make packages for their favorite distros. This has worked very well. Users have packaged `just` for all kinds of distros, and those packages seem to be more or less up to date.

However, packaging for Debian is sufficiently annoying that `just` has still never made it into Debian, even though someone started doing it. I think it was just too annoying.

Given that, I think I should create and maintain the Debian package myself. There are some useful tips on how to do so [here](https://blog.hackeriet.no/packaging-a-rust-project-for-debian/). I might as well do `just` and `imdl` at the same time.