Simplified some parts and reviewed for a correct computation of matrices, considering stereo render view/projection per eye transformations

shaders_rlgl_mesh_instanced -> shaders_mesh_instancing

Co-authored-by: Jeffery Myers <JefMyers@blizzard.com>

Reduce size and better license CC0

* rlDrawMeshInstanced first attempt

* rlDrawMeshInstanced OpenGL 3.3 and VAO checks

* rlDrawMeshInstanced GetShaderAttribLocation; comments

* example instanced shader

* RLGL_STANDALONE RAYMATH_STANDALONE Vector4

* apply suggested naming changes; add instanced mesh example

* remove orphan variables

NB glsl100 shader needs testing on "bare metal"

Co-authored-by: codifies <nospam@antispam.com>

It seems something is not working properly...

Co-authored-by: codifies <nospam@antispam.com>

head can't think of any improvement I could use on the shaders for
version 120
This has been tested on Linux (Desktop) requires testing on a Rpi

Co-authored-by: codifies <nospam@antispam.com>

Tested on Raspberry Pi... Just note that platform is very limited by GPU...

* Removed Unused Uniforms

uniform vec3 viewUp;
uniform float deltaTime;

* Removed Unused uniforms

uniform vec3 viewUp;
uniform float deltaTime;

* Updated Source

  Added   - #define PLATFORM_DESKTOP line for desktop users.
            This now will correctly find the proper glsl version for the raymarching.fs file.
  Removed - Uniforms --> deltaTime and viewUp. Including the code that was setting them.
            They were never used and they were triggering a log warning.
  Removed - The const from both screenWidth and screenHeight.
            Now they can be used to update the shader resolution when screen is resized.
            NOTE : This is a quick fix and probably not the best idea.
  Added   - IsWindowResized() to check if screen is resized.
            If window is resized then width, height and shader resolution are updated.
  Changed - MIT tag at bottom right color value to BLACK. Now it's easier to see.

* Closer Match to original code

* Removed the PLATFORM_DESKTOP Define

Contributed simple shader example

Contributed by ProfJski

Now shader uses `fragTexCoord` that are the full screen texture coordinates normalized, instead of `gl_fragCoord`, the unnormalized screen coordinates

Now dividing by the zoom instead of multiplying (in the shader), so zoom works as expected. Also zoom increase/decrease is now scaled depending on the current zoom.

GLSL 1.10 is typesafe ([PDF specs](https://www.khronos.org/registry/OpenGL/specs/gl/GLSLangSpec.1.10.pdf), page 22), so this shader will not load properly during build.

It's not a super important change, but I came across it while playing with the examples on my pi.

Replaced by medieval 3d assets

Not tested, could have errors