Version 2.1

• Improved unit test coverage
• Refactored to delay computation of pulse shapes to much later in compilation.
  This makes it possible for hardware translators to implement things like SSB,
  amplitude/phase, etc in real-time hardware as opposed to baking it into the
  pulse shape.
• Make it possible to register new hardware translators without directly adding
  the code to PyQLab.
• New migration feature to automatically upgrade configuration files when the
  underlying "schema" changes.
• Adds new Edge channel type to encode connectivity graph of a device. These are
  directed edges, which allows us to emit different instructions based upon the
  directionality of the underlying process. I.e., we can also do CR gates in the
  same direction, but emit different sequences for CNOT(q1, q2) vs CNOT(q2, q1).
• Fixes missing function bodies when using qfunctions.