- Reworked Constraint::Rod to use the distance constraint formulation from Constraint::SphereOnSphereContact. This replaced a "distance squared" constraint for Rod that had poor scaling and didn't play well with other contact constraints.
- Added new methods to Constraint::Rod to make it consistent with newer constraints and usable as a basis for a unilateral "rope" constraint (not implemented yet). Can now modify the end point locations and required length in State.
- Added lots of missing documentation for Rod.
- Doxygen improvements to SphereOnSphereContact.