refactor to allow various gfx backends (work-in-progress)
enable OpenGL3 by default (part of work-in-progress refactor)
fix max osx build
MSVC-specific function calls wrapped in a MSVC-specific macro instead of a Windows-specific one.
add alpha blendering option (disabled by default) using w component of color
add low-level support function demo (test)
Adding virtual destructor for RenderCallbacks struct
Adding virtual dtors to classes in btSoftBody
Merge pull request #268 from kwatts/render_callback_virtual_dtor

Thanks for the help! Adding virtual destructor for RenderCallbacks struct
Adding destructor to GraphicsPhysicsBridge
Virtual dtor for CommonParameterInterface
fix build error in SupportFuncDemo.h
add support to btHingeConstraint to set/get ERP, example use:
hinge->setParam(BT_CONSTRAINT_ERP,0.5);
btScalar erp = hinge->getParam(BT_CONSTRAINT_ERP);
Also, preliminary support for status bar messages in demo framework.
fix double precision build
Merge pull request #271 from erwincoumans/master

 btHingeConstraint to set/get ERP, refactor gfx backends (work-in-progress)
Merge pull request #260 from sippeangelo/issue-260

Microsoft compiler wrongly assumed on Windows platform
Merge pull request #269 from kwatts/render_callback_virtual_dtor

Render callback virtual dtor
Added a basic COLLADA .dae importer mainly to support URDF loading (URDF can refer to COLLADA .dae or STL .stl for mesh support)
It is fairly limited, only supports loading <geometry> with triangulated meshes, no material loading
I will extend this with COLLADA Physics support.
fix mac build
remove unnecessary header
add basic concept demo, Coordinate System for a start.
set the up axis for some of the demos.