This one is for interactive exploring of svg paths.

You can enter an SVG path in the entry and hit Enter
to see how GSK renders it. If you click the button
in the headerbar, you can see what GTK thinks the
closest point, tangent and distance are wrt. to the
mouse position, and the bounding box of the path.

There's also stroke parameters to play with.

It comes in handy, and does no harm.

Add a simple demo for editing a poly-Bezier curve.

Implement offsetting of paths by reusing the
infrastructure of the stroker.

Add a function that takes a path, and offsets it
by some distance, applying line-join parameters
as needed.

This commit just adds the api, the implementation
will be in the following commit.

Move some utility functions around.

Implement arced joins as specified in SVG2.

Implementation will follow.