Add stub packages for description, viz.
Single stepped module description.
Add launcher for visualizing the PTU model in isolation.
Completed basic tf tree and model of D46.
Reduce tf marker sizes so as not to overwhelm the wee model.
General fixes, especially install macros, and building the example urdf at make time.
Merge pull request #12 from ros-drivers/desc

Usable description of the D46.