Add experimental Android support (#190)

* Add `Raylib-cs.Android` project
* Update ci to handle android native libraries
* Update ci to pack android project

Raylib-cs.Android/android.patch

@@ -0,0 +1,27 @@
+diff --git a/src/rcore.c b/src/rcore.c
+index eae4951..4400b22 100644
+--- a/src/rcore.c
++++ b/src/rcore.c
+@@ -1,3 +1,22 @@
++#if defined (PLATFORM_ANDROID)
++#include <stdlib.h>
++
++typedef void (*RaylibAndroidCallback)();
++static RaylibAndroidCallback _androidCallback = NULL;
++
++void RaylibSetAndroidCallback(RaylibAndroidCallback callback) {
++  _androidCallback = callback;
++}
++
++int main(int argc, char *argv[]) {
++  (void)argc;
++  (void)argv;
++  while (_androidCallback == NULL) {
++  }
++  _androidCallback();
++}
++#endif
++
+ /**********************************************************************************************
+ *
+ *   rcore - Basic functions to manage windows, OpenGL context and input on multiple platforms