Fix comments and function arguments

[Giulero]

@GiulioRomualdi spotted some wrong arguments in the pytorch interface.
Fixed joint_position to joint_postions as in the other functions.
Took the occasion also to fix other wrong comments.

Changing also the raise DeprecationWarning for the use of the root_link introduced in #114 to a more mild warning.warn().

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📚 Documentation preview 📚: https://adam-docs--116.org.readthedocs.build/en/116/

[Giulero]

Thanks @GiulioRomualdi ! Merging