change build system to CMake and use SDL3 for everything

libs/SDL3/docs/INTRO-cmake.md

@@ -0,0 +1,50 @@
+
+# Introduction to SDL with CMake
+
+The easiest way to use SDL is to include it as a subproject in your project.
+
+We'll start by creating a simple project to build and run [hello.c](hello.c)
+
+Create the file CMakeLists.txt
+```cmake
+cmake_minimum_required(VERSION 3.16)
+project(hello)
+
+# set the output directory for built objects.
+# This makes sure that the dynamic library goes into the build directory automatically.
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/$<CONFIGURATION>")
+set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/$<CONFIGURATION>")
+
+# This assumes the SDL source is available in vendored/SDL
+add_subdirectory(vendored/SDL EXCLUDE_FROM_ALL)
+
+# Create your game executable target as usual
+add_executable(hello WIN32 hello.c)
+
+# Link to the actual SDL3 library.
+target_link_libraries(hello PRIVATE SDL3::SDL3)
+```
+
+Build:
+```sh
+cmake -S . -B build
+cmake --build build
+```
+
+Run:
+- On Windows the executable is in the build Debug directory:
+```sh
+cd build/Debug
+./hello
+``` 
+- On other platforms the executable is in the build directory:
+```sh
+cd build
+./hello
+```
+
+A more complete example is available at:
+
+https://github.com/Ravbug/sdl3-sample
+
+Additional information and troubleshooting is available in [README-cmake.md](README-cmake.md)