The documentation is missing the definition for plane_symbol helper function

[Niketin]

In the documentation, there is a definition for a helper function location_symbol

build123d/docs/location_arithmetic.rst

Lines 14 to 15 in f22f54a

	def location_symbol(self, l=1) -> Compound:
	return Compound.make_triad(axes_scale=l).locate(self)

and it is used in the following example code.

build123d/docs/location_arithmetic.rst

Line 27 in f22f54a

show_object(location_symbol(loc), name="location")

There is a similar function for planes, plane_symbol, and it is also used in the same way as location_symbol.

build123d/docs/location_arithmetic.rst

Line 40 in f22f54a

show_object(plane_symbol(plane), name="plane")

The problem is that the function's definition is not documented anywhere on the page (or anywhere else as far as I know).