v0.2.2 - Support for polar coordinates in Vector2

New Features

See #34

• Vector2 Constructor accepts polar coordinates (with the optional polar keyword argument)
• Vector2 and Vector3 instances have rho, theta, and theta_deg as properties
• Vector3 instances also have phi and theta_phi as properties

For further discussion on how to generalize some of these changes, especially with regard to dimensionality, see #35

Thank you @Evelyn-H!