Add Plane.reverse() method

[tobywf]

It might be good to add a Plane.reverse() method, analogue to Axis.reverse() and Vector.reverse().

Pros:

• Axis implements both __neg__ and reverse(), Vector implements both __neg__ and reverse(), while Plane currently only implements __neg__.
• I spent longer than I care to admit trying to figure out how to reverse/invert a plane. Plane.reverse() helps with discoverability due to auto-complete.
• A method has a clear operator precedence. -Plane.XY.offset(10.0) applies the offset first, and then the reversal. (-Plane.XY).offset(10.0) is required to first reverse and then offset.Plane.XZ.reverse().offset(10.0) works as intended.

Cons:

• Axis.reverse() corresponds directly to the OCCT method Reversed. Plane.reverse() doesn't; but Vector.reverse() also doesn't.
• There would be two ways to reverse a plane. But that's true of Axis and Vector also.
• There's already Plane.reverse_transform(), which is close in name.
• Could be that e.g. invert() is a more appropriate name.

Overall, I think Plane.reverse() makes sense, but let me know. Looks like an easy PR; happy to submit one if you'd like.

[tobywf]

Example of operator precedence issue:

Plane.reverse = lambda s: -s
print(-Plane.XY.offset(10.0))
print((-Plane.XY).offset(10.0))
print(Plane.XY.reverse().offset(10.0))

Plane(o=(0.00, 0.00, 10.00), x=(1.00, 0.00, 0.00), z=(-0.00, -0.00, -1.00))
Plane(o=(0.00, 0.00, -10.00), x=(1.00, 0.00, 0.00), z=(-0.00, -0.00, -1.00))
Plane(o=(0.00, 0.00, -10.00), x=(1.00, 0.00, 0.00), z=(-0.00, -0.00, -1.00))

[gumyr]

Done.