Add cohesion property to DEM material.
Better backdrop cube map for chrono demos
Improved Irrlicht interface.
- link references can be shown
- symbols scale can be set (open window with 'i' key)
- other improvements
Added support for stiffness matrices (non-diagonal M) in the direct solver.
Added new ChRackpinion class, for rack-pinion constraint.
To be completed (phasing is not checked/enforced, might drift...)
comments changed
New ChBodyEasy classes!
Useful for creating simple spherical / boxy / cylindrical bodies, it automatically does:
1) compute mass & inertia tensor
2) add visualization shape
3) add collision shape if needed.
Bug fix in ChLinkMateGeneric (children classes migh not get time update)
Small refactoring
Removed logging from 'beam' helper class.
Merge remote-tracking branch 'upstream/develop'

Conflicts:
	src/CMakeLists.txt
Merge branch 'master' of https://github.com/jcmadsen/chrono