Move scriptapi to separate folder (by sapier)

On the lua side, notably minetest.env:<function>(<args>) should now
be replaced by minetest.<function>(<args>).
The old way is and will stay supported for a long time.

Also:
Update and clean up lua_api.txt (by celeron55)
Move EnvRef to lua and remove add_rat and add_firefly (by kahrl)
Add separate src/util/CMakeLists.txt, other minor fixes (by kahrl)

src/script/cpp_api/s_env.h

@@ -0,0 +1,40 @@
+/*
+Minetest
+Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#ifndef S_ENV_H_
+#define S_ENV_H_
+
+#include "cpp_api/s_base.h"
+#include "irr_v3d.h"
+
+class ServerEnvironment;
+
+class ScriptApiEnv
+		: virtual public ScriptApiBase
+{
+public:
+	// On environment step
+	void environment_Step(float dtime);
+	// After generating a piece of map
+	void environment_OnGenerated(v3s16 minp, v3s16 maxp,u32 blockseed);
+
+	void initializeEnvironment(ServerEnvironment *env);
+};
+
+#endif /* S_ENV_H_ */