FGO: add keyboard input (#61)

Probably self-explanatory :p

Reviewed-on: TeamTofuShop/segatools#61
Co-authored-by: kyoubate-haruka <46010460+kyoubate-haruka@users.noreply.github.com>
Co-committed-by: kyoubate-haruka <46010460+kyoubate-haruka@users.noreply.github.com>

fgoio/xi.h

@@ -0,0 +1,10 @@
+#pragma once
+
+/* Can't call this xinput.h or it will conflict with <xinput.h> */
+
+#include <windows.h>
+
+#include "fgoio/backend.h"
+#include "fgoio/config.h"
+
+HRESULT fgo_xi_init(const struct fgo_xi_config *cfg, const struct fgo_io_backend **backend);