test and build packages in their own systems

[FWDekker]

currently all linux builds are produced and tested on linux. but that's not good enough. it should be built and tested in the system for which it will build (e.g. run in an archlinux vm, download the aur repo, point it to the current branch, run and test makepkg), to make sure it really works end-to-end.

[FWDekker]

the whole aur stuff is now tested in an archlinux docker image, so that goal has been reached.

whether to also build rpm in a fedora distribution, well, that's a question for later, for once #39 has been implemented. once sufficient repositories have been added, the fpm-created packages will eventually disappear, and this issue will then have been implemented.