* Updated rcore.c, renamed 'time' to 'time_nsec'
When PLATFORM_ANDROID, PLATFORM_RPI or PLATFORM_DRM were defined, there is a compilation error to redefinition of the variable 'time', so the second instance of 'time' was changed to 'time_nsec' which both fixes the name collision and more accurately describes what that variable represents.
* Renamed 'time_nsec' to 'nanoSeconds'
Added a comment explaining the range limitations of GetRandomValue.
Added a run-time warning TRACELOG when GetRandomValue is called with an invalid range.
Those two functions have been moved to a new example: `models_draw_cube_texture`. The reasons for this decision:
- Function inflexibility: Many users with the need to draw a textured cube could need to customize the texture applied to every face, that function did not allow that kind of functionality.
- rlgl functionality exposure: The implementation exposed will teach users how to implement custom textured triangles drawing.
This function can be easely replicated using `DrawtexturePro()` and actually it was doing some assumptions not transparent to the user. Even the function name was confusing. No example was available for it and actually noone requested one example.
* build.zig: let user decide how to set build mode
This should delegate the responsibility of calling `standardReleaseOptions` and setting the build mode of the `*LibExeObjStep` step to the caller, especially since this might not be the process by which one wants to determine the build mode.
Also changes hides `getSrcDir` to enforce usage of `srcdir`, and asserts that the file is in fact inside a directory.
* build.zig: set root_src param to `null`
Supplying the header file as the root source here appears to cause a linker warning of the form:
```
LLD Link... warning(link): unexpected LLD stderr:
ld.lld: warning: {build_root}/zig-cache/o/{hash}/libraylib.a: archive member '{build_root}/zig-cache/o/{hash}/raylib.o' is neither ET_REL nor LLVM bitcode
```
Passing `null` instead fixes it.
* Use RL_QUADS/RL_TRIANGLES for single-pixel drawing
Addresses problem mentioned in
https://github.com/raysan5/raylib/issues/2744#issuecomment-1273568263
(in short: when drawing pixels using DrawPixel{,V} in camera mode,
upscaled pixel becomes a line instead of bigger pixel)
* [rtextures] Fixed scaling down in ImageTextEx
Closes#2755
