v0.2.1

• Arithmetic on Direction produces an UnnormalizedDirection, which can be converted back to a
  regular normalized Direction. This allows intermediate operations to be unnormalized before
  explicitly normalizing at the last step.
• Experimental (unexported) support for rotation matrices.
• Julia will no longer crash when trying to operate on a closed table. This used to occur because
  the C++ code throws an exception. Now Julia will throw an exception instead.