[client] added renderer abstratction

This moves the bulk of the rendering code into seperate rendering
modules cleaning up much of intertwined SDL & OpenGL mess.

client/lg-renderers.h

@@ -0,0 +1,30 @@
+/*
+Looking Glass - KVM FrameRelay (KVMFR) Client
+Copyright (C) 2017 Geoffrey McRae <geoff@hostfission.com>
+
+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, write to the Free Software Foundation, Inc., 59 Temple
+Place, Suite 330, Boston, MA 02111-1307 USA
+*/
+
+#pragma once
+#include "lg-renderer.h"
+
+extern const LG_Renderer LGR_OpenGL;
+extern const LG_Renderer LGR_Basic;
+
+const LG_Renderer * LG_Renderers[] =
+{
+  &LGR_OpenGL,
+  &LGR_Basic,
+  NULL // end of array sentinal
+};