Python: Introduce gdb.Instruction class

This adds a generic instruction class to Python and has gdb.RecordInstruction
inherit from it.

gdb/python/py-instruction.h

@@ -0,0 +1,30 @@
+/* Python interface to instruction objects.
+
+   Copyright 2017 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 3 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://www.gnu.org/licenses/>.  */
+
+#ifndef GDB_PY_INSTRUCTION_H
+#define GDB_PY_INSTRUCTION_H
+
+#include "python-internal.h"
+
+/* Python type object for the abstract gdb.Instruction class.  This class
+   contains getters for four elements: "pc" (int), "data" (buffer), "decode"
+   (str) and "size" (int) that must be overriden by sub classes.  */
+extern PyTypeObject py_insn_type;
+
+#endif /* GDB_PY_INSTRUCTION_H */