Setup automatic versioning based on Git

[gipert]

I remember giving up on implementing this properly in the early times because of some annoying problem (but I cannot remember now). We should definitely fix this.

[ManuelHu]

what is still needed?

• docker hub builds (use the right version after Fix Dockerfile versioning strategy #171)
• documentation should be correct after test more RTD changes #159)
• local builds in remage CLI output and libremage sonames?