Add an explicit example for registering function overloads via fake-jni

[Matthewacon]

using namespace FakeJni;

struct NativeClass {
 DEFINE_CLASS_NAME("com/example/NativeClass")

 void func() {}
 void func(JInt) {}
};

BEGIN_NATIVE_DESCRIPTOR(NativeClass)
 {Constructor<NativeClass> {}},
 {(void (*)())&NativeClass::func, "func"},
 {(void (*)(JInt))&NativeClass::func, "func"}
END_NATIVE_DESCRIPTOR