v0.2.1

Added

• pystudio --version.

Fixed

• pystudio --demo after a plain install now says the tour needs numpy, pandas
  and matplotlib and how to install them, instead of starting and failing at
  the first import. The check used to run only for a project environment.
• Quitting while the kernel is still starting no longer ends in a traceback.
• Closing the agent pane no longer fails on macOS when its program has already
  exited.