make kuhl_errorcheck() work better with cpp
use include guards and extern C in all headers
fix typo in comment, use quotes in CMakeLists
remove unnecessary/misleading information from shader programs
add diffuse shading example for opengl 3
Fixed Doxy Build for CLion IDE
Merge remote-tracking branch 'upstream/master'
improve description of ogl3-assimp shaders
add comment to cmakelists
make orthographic projection matrix match version in redbook appendix
fix normal matrix calculations
fix normal matrix in ogl3-assimp example
move MAGICKCORE preprocessor declarations to get rid of warnings on some systems
add additional error checks in kuhl_print_program_info()
fix mistake in ogl3-assimp.vert
improve kuhl_geometry_init/draw documentation; minor adjustments; do a better job of disabling glsl program when don't need it anymore
mat3*_scale*_new() functions that were missing from kuhl-util.h
Fix a few issues with building on OSX

NOTE: The version of OpenGL shipping with OSX only really supports the
OGL2 examples for now. I haven't been able to completely figure out why
the OGL3 examples just die.
Small changes in help to clarify these build on OSX.
Merge pull request #1 from belak/master

Kaleb's fixes for building on OSX