PEP 440 compliance of get_version_from_git
Right now it someone installs a development version of Kwant, it will identify itself as e.g.
1.2.2 is the most recent available git tag. This is not correct, because by PEP 440, this means that this code will be release as 1.2.2. In other words,
1.2.2.dev21+g9c313bb < 1.2.2.