strdup() is not a C99 function (it's POSIX), not available in emscripten

On OpenGL ES it was set to use GL_CLAMP_TO_EDGE wrap mode for textures.
On LoadOBJ() texture coordinates were wrongly Y-flipped

Shaders come in two flavours:
- shaders/gl330: OpenGL 3.3+ (Windows, Linux, OSX)
- shaders/gles100:  OpenGL ES 2.0 (Android, RPI, HTML5)

[rlgl] Extensions strings loading was redone to avoid a Segmentation
Fault on Raspberry Pi

Merged branch 'master' into develop and remerged to master

Develop branch integration

Splitted into:
UpdateCamera()             // Update only camera
UpdateCameraPlayer()   // Update camera and player position

Probably more useful...

Immediate Mode GUI (IMGUI)

Cat replaced by dwarf

- Trying to implement rlglUnproject() - NOT WORKING
- Tested GLEW alternatives: glad and glLoadGen - NOT WORKING