add gfx.weather library & add weather.set command

res/presets/weather/clear.json

@@ -0,0 +1 @@
+{}

res/presets/weather/fog.json

@@ -1,5 +1,5 @@
 {
-    "fog_opacity": 0.99,
+    "fog_opacity": 0.98,
     "fog_dencity": 3.6,
     "fog_curve": 0.25,
     "clouds": 0.8

res/scripts/stdcmd.lua

@@ -264,6 +264,20 @@ console.add_command(
     end
 )
 
+console.add_command(
+    "weather.set name:str time:num=1",
+    "Change weather",
+    function (args, kwargs)
+        local filename = file.find("presets/weather/"..args[1]..".json")
+        if not filename then
+            return "weather preset not found"
+        end
+        local preset = json.parse(file.read(filename))
+        gfx.weather.change(preset, args[2])
+        return "weather set to "..filename.." preset ("..tostring(args[2]).." s)"
+    end
+)
+
 console.cheats = {
     "blocks.fill",
     "tp",
@@ -271,5 +285,6 @@ console.cheats = {
     "time.set",
     "time.daycycle",
     "entity.despawn",
-    "player.respawn"
+    "player.respawn",
+    "weather.set",
 }