Update docs for maximal_[centered|]_bounded_sphere

[janbridley]

Feature description

Confusion often arises between the maximal bounded sphere and the minimal bounding sphere.

Proposed solution

The docs for these properties should be updated to be more specific. Perhaps graphical examples could be given to clarify the confusing wording. insphere_from_center (the previous property name) is perhaps more misleading - an "insphere", which by Coxeter's definition must be tangent to every face, is not the same as the general bounded sphere discussed above.