Reorganize project file structure

- Create separate directories for source and header files.
- Build code shared between xsystem4 and aindump as a static library.
- Create header dirs gfx/ system4/ and vm/
- Make CG.c/h usable without a running VM

include/debugger.h

@@ -0,0 +1,26 @@
+/* Copyright (C) 2019 Nunuhara Cabbage <nunuhara@haniwa.technology>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://gnu.org/licenses/>.
+ */
+
+#ifndef SYSTEM4_DEBUGGER_H
+#define SYSTEM4_DEBUGGER_H
+#ifdef DEBUGGER_ENABLED
+
+void dbg_init(void);
+void dbg_fini(void);
+void dbg_repl(void);
+
+#endif /* DEBUGGER_ENABLED */
+#endif /* SYSTEM4_DEBUGGER_H */