Merge pull request #13 from fairlight1337/master

Just a few details; exporting symbols, adding an object-adder, updating .gitignore
Added functions to create a urdf description from a robot model
Exported generate-urdf
Forgot a ',' and to check if the limits are unbound
Added unit-tests and test-urdfs
Fixes for the pr2.urdf
Fixes for the quaternion to euler conversion
Fixes for mesh scale and nameless materials.
Changed the filepath from meshes and textures from an absolute path to the one from the urdf.
Merge pull request #14 from jannikb/master

Added robot to urdf funtion to cl_urdf