- removed AntTweakBar GUI - added imgui - added PLY export - added documentation of scene file format

- added XPBD FEM constraint for deformable solids - updated to Eigen 3.4.0

Merge pull request InteractiveComputerGraphics#114 from InteractiveCo… …mputerGraphics/python_bindings Python bindings

- added substepping - added OBJ export

- added DamperJoint - improved implementation of SliderJoint - improved implementation of TargetPositionMotorSliderJoint - improved implementation of TargetVelocityMotorSliderJoint - improved implementation of HingeJoint - improved implementation of TargetAngleMotorHingeJoint - improved implementation of TargetVelocityMotorHingeJoint

- added collision detection for arbitrary meshes based on cubic signe… …d distance fields - added Discregrid library as external project to generate cubic signed distance fields

- bugfix 

- updated README.md 

- added TargetVelocityMotorHingeJoint - added TargetAngleMotorHingeJoint - extended JointDemo - made function names consistent

- added documentation