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.

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index 6d359379e..297566068 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -2089,7 +2089,9 @@ and `minetest.auth_reload` call the authetification handler.
       given biome_name string.
 * `minetest.get_mapgen_params()` Returns mapgen parameters, a table containing
   `mgname`, `seed`, `chunksize`, `water_level`, and `flags`.
+  * Deprecated: use minetest.get_mapgen_setting(name) instead
 * `minetest.set_mapgen_params(MapgenParams)`
+    * Deprecated: use minetest.set_mapgen_setting(name, value, override) instead
     * Set map generation parameters
     * Function cannot be called after the registration period; only initialization
       and `on_mapgen_init`
@@ -2099,6 +2101,23 @@ and `minetest.auth_reload` call the authetification handler.
         * `flags` contains a comma-delimited string of flags to set,
           or if the prefix `"no"` is attached, clears instead.
         * `flags` is in the same format and has the same options as `mg_flags` in `minetest.conf`
+* `minetest.get_mapgen_setting(name)`
+    * Gets the *active* mapgen setting (or nil if none exists) in string format with the following
+      order of precedence:
+        1) Settings loaded from map_meta.txt or overrides set during mod execution
+        2) Settings set by mods without a metafile override
+        3) Settings explicitly set in the user config file, minetest.conf
+        4) Settings set as the user config default
+* `minetest.get_mapgen_setting_noiseparams(name)`
+    * Same as above, but returns the value as a NoiseParams table if the setting `name` exists
+      and is a valid NoiseParams
+* `minetest.set_mapgen_setting(name, value, [override_meta=false])`
+   * Sets a mapgen param to `value`, and will take effect if the corresponding mapgen setting
+     is not already present in map_meta.txt.  If the optional boolean override_meta is set to true,
+     this setting will become the active setting regardless of the map metafile contents.
+   * Note: to set the seed, use "seed", not "fixed_map_seed"
+* `minetest.set_mapgen_setting_noiseparams(name, value, [override_meta=false])`
+   * Same as above, except value is a NoiseParams table
 * `minetest.set_noiseparams(name, noiseparams, set_default)`
     * Sets the noiseparams setting of `name` to the noiseparams table specified in `noiseparams`.
     * `set_default` is an optional boolean (default: `true`) that specifies whether the setting