Allow use of main instead of android_main

Inspired by #504.
Instead of requiring the user to do PLATFORM_ANDROID #ifdefery,
have the android_main entry point exported by raylib and call
the user-defined main. This way many games could (in theory)
run unmodified on Android and elsewhere.

This is untested!

games/tetris.c

@@ -18,10 +18,6 @@
 #include <time.h>
 #include <math.h>
 
-#if defined(PLATFORM_ANDROID)
-    #include "android_native_app_glue.h"
-#endif
-
 #if defined(PLATFORM_WEB)
     #include <emscripten/emscripten.h>
 #endif
@@ -109,19 +105,11 @@ static void DeleteCompleteLines();
 //------------------------------------------------------------------------------------
 // Program main entry point
 //------------------------------------------------------------------------------------
-#if defined(PLATFORM_ANDROID)
-void android_main(struct android_app *app) 
-#else
 int main(void)
-#endif
 {
-    // Initialization
+    // Initialization (Note windowTitle is unused on Android)
     //---------------------------------------------------------
-#if defined(PLATFORM_ANDROID)
-    InitWindow(screenWidth, screenHeight, app);
-#else
     InitWindow(screenWidth, screenHeight, "sample game: tetris");
-#endif
 
     InitGame();
 
@@ -148,9 +136,8 @@ int main(void)
     
     CloseWindow();        // Close window and OpenGL context
     //--------------------------------------------------------------------------------------
-#if !defined(PLATFORM_ANDROID)
+
     return 0;
-#endif
 }
 
 //--------------------------------------------------------------------------------------
@@ -841,4 +828,4 @@ static void DeleteCompleteLines()
             }
         }
     }
-}
+}