0.13.0

What's Changed

• Add a python3 shim on windows. Previously entering python3 in the
  command line would always bring up the windows store python proxy even
  when global shims were enabled. As virtualenvs do not support the
  python3 executable on windows, the internal shim handling is now also
  changed so that trying to launch python3 will fall back to python.
  This makes it possible to run maturin build.

• Add maturin build command to start a new maturin PyO3 project.

Full Changelog: 0.12.0...0.13.0