Doxygen description edits for Joint, including new gifs

I don't know what you mean....

On Tue, Nov 11, 2014 at 2:50 PM, Tom Uchida <notifications@github.com>
wrote:

> In OpenSim/Simulation/SimbodyEngine/BallJoint.h:
>
> > @@ -34,12 +34,14 @@ class Model;
> >  //=============================================================================
> >  //=============================================================================
> >  /**
> > - * A class implementing an Ball joint.  The underlying implementation
> > - * in Simbody is a MobilizedBody::Ball.
> > - *
> > - * @author Ajay Seth
> > - * @version 1.0
> > - */
> > +
> > +A class implementing a Ball joint. The underlying implementation in Simbody is SimTK::MobilizedBody::Ball. The OpenSim Ball joint implements a fixed 1-2-3 (X-Y-Z) body-fixed Euler sequence, without translations, for generalized coordinate calculation. Ball joint uses quaternions in calculation and are therefore singularity-free (unlike GimbalJoint). Generalized speeds are equal to the computed angular velocities (\f$\vec{u} = \vec{\omega}\f$), not a differentiation of position (\f$\vec{u} \neq \dot{\vec{q}}\f$)
>
> Line break after 80 characters?
>
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> <https://github.com/opensim-org/opensim-core/pull/257/files#r20187850>.
>