Log Message:
Spiro is the creation of Raph Levien. It simplifies the drawing of beautiful
curves.

Using bezier splines an artist can easily draw curves with the same slope on
either side of an on-curve point. Spiros, on the other hand, are based on
clothoid splines which make it easy to maintain constant curvature as well as
constant slope. Such curves will simply look nicer.

Raph Levien's spiro splines only use on-curve points and so are easier to use
and more intuitive to the artist.

This library will take an array of spiro control points and convert them into
a series of bezier splines which can then be used in the myriad of ways the
world has come to use beziers.