This is an efficient C++ implementation of the Cassowary constraint
solving algorithm. Kiwi(solver) is an implementation of the algorithm
based on the seminal Cassowary paper. It is not a refactoring of the
original C++ solver.  Kiwi(solver) has been designed from the ground
up to be lightweight and fast.  It ranges from 10x to 500x faster than
the original Cassowary solver with typical use cases gaining a 40x
improvement. Memory savings are consistently > 5x.