Update CMake to a more modern module management system and create simple test based on imgui null example

test/main.c

@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <assert.h>
+#include <cimgui.h>
+
+int main(void)
+{
+  assert(igDebugCheckVersionAndDataLayout(igGetVersion(), sizeof(ImGuiIO), sizeof(ImGuiStyle),
+                                          sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert),
+                                          sizeof(ImDrawIdx)));
+  printf("CreateContext() - v%s\n", igGetVersion());
+  igCreateContext(NULL);
+  ImGuiIO *io = igGetIO();
+
+  unsigned char *text_pixels = NULL;
+  int text_w, text_h;
+  ImFontAtlas_GetTexDataAsRGBA32(io->Fonts, &text_pixels, &text_w, &text_h, NULL);
+
+  for (int n = 0; n < 20; n++) {
+    printf("NewFrame() %d\n", n);
+
+    ImVec2 display_size;
+    display_size.x = 1920;
+    display_size.y = 1080;
+    io->DisplaySize = display_size;
+    io->DeltaTime = 1.0f / 60.0f;
+    igNewFrame();
+
+    static float f = 0.0f;
+    igText("Hello World!");
+    igSliderFloat("float", &f, 0.0f, 1.0f, "%.3f", 1.0f);
+    igText("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / io->Framerate, io->Framerate);
+    igShowDemoWindow(NULL);
+
+    igRender();
+  }
+
+  printf("DestroyContext()\n");
+  igDestroyContext(NULL);
+
+  return 0;
+}