Port existing IK latex documentation to InverseKinematics class in-source docs

[traversaro]

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Port existing IK latex documentation to InverseKinematics class in-source docs

[traversaro]

The available documentation from @francesco-romano is this one: romano_ik.zip, even if I am not sure if this is the latest version.

[prashanthr05]

Here's the pdf, just in case if someone wants a quick link,

romano_ik.pdf

P.S. The date got updated to April 2 2021, but it's a relatively old document.

[traversaro]

Thanks!