Sketch Snap Features, Draft improvement, Assembly Section

This release significantly expands on the capabilities of cadquery Sketch. The extended Sketch methods are: text(), val(), vals(), add(), mirror_x(), mirror_y(), spline(), polyline(), center_arc(), tangent_arc(), three_point_arc(), bounding_box(), push_points(). All of these methods take "snaps" for point or tangent inputs, where snaps are text strings in the form "@" where position can be a float between 0 and 1 or "start", "middle", or "end". Also note that these methods accept sequences directly, like .polyline((-1, 0), (1, 1), (2, 0), (3, 1), (4, 0)) without the need to wrap the points in a list.

The drafting package has a new feature. One can now create horizontal/vertical extension lines for diagonal features as shown on the right (the left side was previous functionality):

Assembly has a new section() method. It generates a new assembly that is a cross section of the original assembly for the given plane maintaining the object names and colours.