This is a starting point; no dashes, only butt and miter.

Also not tested yet.

Will close #285

Fix some todo() items. Reverse forward and backward so area is positive. Implement line caps and joins.

Make end_point a public method of `PathEl`, as suggested.

Dashes remain, as well as closed paths.

Handle stroking of closed subpaths. This generates two closed subpaths as output, one for the inner contour, one for the outer.

Also apply a threshold for joins.

This should handle closed paths and phase, but do need to validate.

Add an additional argument to stroke expansion. It's designed so it can be Default::default() in the common case, and uses the builder pattern to add more options as needed without breaking semver.

Wire up regularization in parallel curve generation (now merged into branch). Fix zero length segment detection (it was overly eager, also triggering on degenerate tangents).

In response to review comments.