Make NN command line work

[patatepartie]

This PR includes commits from https://github.com/metterklume/chessputzer/pull/4 because I didn't want to fork from a fork, especially since the mentioned PR has been opened for a long time and is not likely to be merged (either).

It should fix this issue too: https://github.com/metterklume/chessputzer/issues/5

Following the instructions in the doc should work now. I had to install libgl1 to have it working (apt-get update && apt-get install -y --no-install-recommends libgl1 on debian/ubuntu).