Transformation: initial work for Transformation matrix

This adds Transformation, a transformation matrix object.

This is an affine transformation matrix, which supports translate,
rotate, and scale out of the box (similar to Cairo). Additionally, you
can supply your own transformations by initializing your own
transformation, and multiplying it against an existing matrix.

Methods exist for transforming co-ordinates between user space (e.g.,
the co-ordinates and figures you supply to Path and future similar
interfaces) and device space (what ultimately gets recorded to write to
the surface), and vice-versa (applying the inverse). Methods also exist
for transforming distance (which skip the translation vector). The
distance methods are particularly important during the plotting phase
where we need to use distance to transform line widths and pen radii.

Next steps to follow: Adding transformations to Path.