Automate docs generation and release

[Johannes Demel]

We use doxygen to produce our docs. We should be able to automatically build the docs and deploy them.
@noc0lour mentioned:

  - run: 'tar -cz public | ssh $SSH_USER@$SSH_HOST "mkdir -p /www/$(date +%Y.%m.%d); cd /www/$(date +%Y.%m.%d); tar --strip-components=1 -xz; rm /www/live; cd /www; ln -sf $(date +%Y.%m.%d) live;"'

from: https://github.com/gnuradio/libvolk.org/blob/master/.circleci/config.yml

I suggest to regenerate the docs everytime a push/merge to main happens.

[Andrej Rode]

I can quickly configure the webspace such that uploading to the libvolk.org documentation is possible from the pipeline.