Instance properties (w, x, y, z) for quaternion components

[varunagrawal]

Added properties to the Quaternion class to allow access to individual quaternion components in a clean, notational manner.

[KieranWynn]

Hi Varun This looks good. Initially I was against assigning particular identifiers to the elements of the Quaternion object because, in theory, you could use any 4 consecutive letters to refer to the same thing e.g. [a, b, c, d]. I think though, after seeing how prevalent the convention of [w, x, y, z] is this actually makes more sense than not, and will be a handy feature. Thanks for your contribution. :)