Rewrites documentation for rotate3_inertia and renames to relevant functions.

The rotate3_inertia's documentation defined the rotation matrix as v_a = R *
v_b but what it actually returned seemed to be from the definition v_b = R *
v_a. I updated the documentation to reflect this and altered the
Human.inertia_transformed to return what it's documentation says it returns.
Finally I renamed rotate3_inertia to rotate_inertia and switched the order of
the arguments and I renamed Human.inertia_transformed to
Human.transform_inertia so that the name is a verb indicating what the method
does rather than what it returns. Both of these have deprecation warnings so
the old names can be used until Yeadon 2.0. I also moved the deprecation
warning to it's own module so that it can be more easily used in all the
modules with no chance of circular dependencies.
Ignore deprecation warnings in tests.
Added simple test for rotate_inertia.
Fixed test error, missing negative on products of inertia.
Added test for rotate_inertia and updated docs.
Fixed typos and wording.
Noted that the rotation matrix is the transpose.