The documentation now correctly describes the behavior of the ``parts``
option in an inheritance-diagram directive: it gives the number of parts
that are *kept* not dropped. The option now also accepts negative
values, which drops parts from the left (which is the what the
documentation incorrectly claimed the option would do for positive
values)
As a form of testing of the new functionality, the documentation for the
inheritance_diagram extension now includes a section "Examples" that
demonstrate the different possibilities. This would fail to build
without the patch.
Closes#4872