* explained a bit more the core_window_letterbox example

* fixed a few 'ups' moments that could lead to mild head pain and time loss

* new linux makefile for Android portages

* Revert "projects: CMake: bump up minimal raylib version (#983)"

This reverts commit 82306af111.

* new PR for upstream

* for Raysan

ADDED: CodepointToUtf8()

RENAMED: TextCountCodepoints() -> GetCodepointsCount()

* 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

* Initial commit of addition for GLTF materials.. should support loading more than just albedo map.

* Clean up

* fixed seg faults and leaks

* temp don't overwrite defuse colour when rendering

* undid something dumb!

* correctly mixed diffuse map color when rendering to preserve not overwrite it

- Improved LoadBMFont()

Now it accepts a ';' separated list of extensions, useful to check multiple extensions

Get the unicode equivalent characters (as int array) from a UTF-8 text array... maybe this function is renamed to be clearer to users...

When adding alpha mask to GRAYSCALE image, if using ImageFormat(), it could change pixel values, now we avoid that, mask is just added as an extra channel

While at it, add comment to indicate what the version signifies.

[a3f: updated commit message]

The result of `success` is actually never used. Either we should check
for it and return or remove it. I assume just checking the last one is
okay.

* Const corectness for LoadShaderCode

* Added const for standalone variant as well.

Contributed simple shader example

Still looking for a better way to integrate it into raylib API, maybe add a LoadImageAnim()?