Add MapSettingsManager and new mapgen setting script API functions

This commit refactors the majority of the Mapgen settings system.
- MapgenParams is now owned by MapSettingsManager, itself a part of ServerMap,
  instead of the EmergeManager.
- New Script API functions added:
    core.get_mapgen_setting
    core.get_mapgen_setting_noiseparams,
    core.set_mapgen_setting, and
    core.set_mapgen_setting_noiseparams.
- minetest.get/set_mapgen_params are deprecated by the above new functions.
- It is now possible to view and modify any arbitrary mapgen setting from a mod,
  rather than the base MapgenParams structure.
- MapgenSpecificParams has been removed.

src/map_settings_manager.h

@@ -0,0 +1,79 @@
+/*
+Minetest
+Copyright (C) 2010-2013 kwolekr, Ryan Kwolek <kwolekr@minetest.net>
+
+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 MAP_SETTINGS_MANAGER_HEADER
+#define MAP_SETTINGS_MANAGER_HEADER
+
+#include <string>
+
+class Settings;
+struct NoiseParams;
+struct MapgenParams;
+
+/*
+	MapSettingsManager is a centralized object for management (creating,
+	loading, storing, saving, etc.) of config settings related to the Map.
+
+	It has two phases: the initial r/w "gather and modify settings" state, and
+	the final r/o "read and save settings" state.
+
+	The typical use case is, in order, as follows:
+	- Create a MapSettingsManager object
+	- Try to load map metadata into it from the metadata file
+	- Manually view and modify the current configuration as desired through a
+	  Settings-like interface
+	- When all modifications are finished, create a 'Parameters' object
+	  containing the finalized, active parameters.  This could be passed along
+	  to whichever Map-related objects that may require it.
+	- Save these active settings to the metadata file when requested
+*/
+class MapSettingsManager {
+public:
+	// Finalized map generation parameters
+	MapgenParams *mapgen_params;
+
+	MapSettingsManager(Settings *user_settings,
+		const std::string &map_meta_path);
+	~MapSettingsManager();
+
+	bool getMapSetting(const std::string &name, std::string *value_out);
+
+	bool getMapSettingNoiseParams(
+		const std::string &name, NoiseParams *value_out);
+
+	// Note: Map config becomes read-only after makeMapgenParams() gets called
+	// (i.e. mapgen_params is non-NULL).  Attempts to set map config after
+	// params have been finalized will result in failure.
+	bool setMapSetting(const std::string &name,
+		const std::string &value, bool override_meta = false);
+
+	bool setMapSettingNoiseParams(const std::string &name,
+		const NoiseParams *value, bool override_meta = false);
+
+	bool loadMapMeta();
+	bool saveMapMeta();
+	MapgenParams *makeMapgenParams();
+
+private:
+	std::string m_map_meta_path;
+	Settings *m_map_settings;
+	Settings *m_user_settings;
+};
+
+#endif