Fixes

[magistermaks]

I found your repo when i was looking for a minimal C++ physics library for my project. In the current state it didn't really work at all so before I could test it I needed to make some changes and decided to try sharing them here. The changes I made:

• Fixed compile time error caused by std::tuple<int, int, int> having no hash function, switched to glm::ivec3
• Fixed linking error caused by invalid function signatures in definition vs. declaration.
• Fixed runtime error caused by not being able to find shaders, i just hardcoded the shader code into the program, imo that is simpler and much less error prone esp. with such simple shaders. Another fix would be to add a CMake task that copies the shaders from ./src into the CMAKE_BUILD_DIR, but that was more work and I wanted to focus on physics.
• Split the graphics code from the physics code (The CMake linked the physics stuff together with graphics libs so I split that as part of trying to use it as a library). This required some changes around Mesh, now the Mesh class lives in physics/ with a tiny bit of graphics code (see physics/mesh.hpp). I wanted to make the separation better in the future but at least it works right now as-is.
• Split the CMake graphic libs into a separate pheV3_graphics target
• Added a "headless" demo that checks if the lib compiles without graphics libs
• Rewrote the box stacking demo to actually test box stacking.
• Fixed collisions a bit to correct the position, making box stacking (somewhat) possible
• Fix demos being dependent on window creation time, making them much more consistent.
• Temporarily removed broadPhaseFilter from PhysicsWorld::update as it did not work (and I had no need for this optimization in my use-case)
• While at it, I also renamed some files to all-lowercase.

There where probably some other changes I missed here,
Kind regards.