Integrate NAR build in liblouis itself

[bertfrees]

See also liblouis/liblouis#314: By supporting NAR in the main liblouis build I would not have to maintain a separate project and update the src directory to the latest Liblouis all the time, and the hacks to modify the configure.ac and liblouis.pc.in files could also be done properly.

EDIT: also the Dockerfile would not have to be duplicated.

[bertfrees]

Note that the releasing part would still be a separate, manual process though. I would probably be responsible for it because Christian can't produce the MacOS build and there is no way to have an automatic build for it on a server.

Update: Releasing is now done by a Github workflow, also for macOS.