Polliwog

- `Polyline.cut_by_plane()`: Handle vertices which lie in the plane.

- Add `segment.segment.closest_point_of_line_segment()`
- Add `line.functions.project_to_line()`

- Polyline:
- Add `num_v` and `num_e` properties.
- Remove `as_lines()` and references to lace.
- Refactor `segment_lengths` using `vg.euclidean_distance()`.
- Vectorize `partition_by_length()`.
- Fix `inflection_points` and add test coverage.
- Add `tri.arity.quads_to_tris()` (from lace).
- Add vectorized plane functions.
- Improve test coverage.
- Don't ship the tests.

- Polyline: Add `bisect_edges()` method.
- Return `np.ndarray`s from shapes functions.

- Add Line primitive.
- Add `polliwog.tri.contains.planar_point`.
- Update vg dependency (now requires 1.2.0).

- Update vg dependency (now requires 1.0.0)