Added library for items commonly shared among tools.

- lib/Makefile.common: common makefile rules for USB tools
- include/f32xbase/usb.h, lib/usb.c: library with the common open_usb
  function

include/f32xbase/usb.h

@@ -0,0 +1,23 @@
+/*
+ * include/f32xbase/usb.h - Common USB code for F32Xbase tools
+ *
+ * Written 2008-2010 by Werner Almesberger
+ * Copyright 2008-2010 Werner Almesberger
+ *
+ * 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.
+ */
+
+
+#ifndef F32XBASE_USB_H
+#define F32XBASE_USB_H
+
+#include <usb.h>
+
+
+usb_dev_handle *open_usb(uint16_t default_vendor, uint16_t default_product);
+void parse_usb_id(const char *id);
+
+#endif /* !F32XBASE_USB_H */