feat: add initial People Playground mod development kit

extracted_wiki_content/snippets/custom_human_sprite.txt

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+URL: https://wiki.studiominus.nl/snippets/customHuman.html
+Title: People Playground Modding - Custom human sprite
+==================================================
+
+Custom human sprite
+This code snippet shows how to create a human with custom sprites. This also works on Gorses and Androids. Very useful if you want to create a mind-numbingly boring mod.
+// register item to the mod registry
+ModAPI.Register(
+    new Modification()
+    {
+        OriginalItem = ModAPI.FindSpawnable("Human"), //item to derive from
+        NameOverride = "Human but blue -BH", //new item name with a suffix to assure it is globally unique
+        DescriptionOverride = "From avatar!!!! (the one with the blue people).", //new item description
+        CategoryOverride = ModAPI.FindCategory("Entities"), //new item category
+        ThumbnailOverride = ModAPI.LoadSprite("blueMan.png"), //new item thumbnail (relative path)
+        AfterSpawn = (Instance) => //all code in the AfterSpawn delegate will be executed when the item is spawned
+        {
+            //load textures for each layer (see Human textures folder in this repository)
+            var skin = ModAPI.LoadTexture("blueSkin.png");
+            var flesh = ModAPI.LoadTexture("blueFlesh.png");
+            var bone = ModAPI.LoadTexture("blueBone.png");
+
+            //get person
+            var person = Instance.GetComponent<PersonBehaviour>();
+
+            //use the helper function to set each texture
+            //parameters are as follows: 
+            //  skin texture, flesh texture, bone texture, sprite scale
+            //you can pass "null" to fall back to the original texture
+            person.SetBodyTextures(skin, flesh, bone, 1);
+
+            //change procedural damage colours if they interfere with your texture (rgb 0-255)
+            person.SetBruiseColor(86, 62, 130); //main bruise colour. purple-ish by default
+            person.SetSecondBruiseColor(154, 0, 7); //second bruise colour. red by default
+            person.SetThirdBruiseColor(207, 206, 120); // third bruise colour. light yellow by default
+            person.SetRottenColour(202, 199, 104); // rotten/zombie colour. light yellow/green by default
+            person.SetBloodColour(108, 0, 4); // blood colour. dark red by default. note that this does not change decal nor particle effect colours. it only affects the procedural blood color which may or may not be rendered
+        }
+    }
+);