Keep the readable renderings out of the world directories

A generated <world>/ is meant to drop straight into a save, and Scribe's smoke
harness copies a data set's contents into a server's world wholesale -- so
anything beside customnpcs/ would be copied in too. The NBTJsonUtil renderings
move to _readable/<world>/ at the output root, which makes each world directory
usable as a cnpc_data_sets overlay with no filtering step.

src/fixtures/java/kamkeel/npcs/fixtures/Readme.java

@@ -30,15 +30,17 @@ public final class Readme {
         sb.append("## Layout\n\n");
         sb.append("```\n");
         for (FixtureWorld world : worlds) {
-            sb.append(world.name()).append("/\n");
-            sb.append("  customnpcs/   <- exactly a CustomNPC+ world directory, and nothing else\n");
-            sb.append("  _readable/    <- NBTJsonUtil renderings of the .dat files, for humans\n");
+            sb.append(world.name()).append("/customnpcs/    <- a CustomNPC+ world directory, and nothing else\n");
         }
-        sb.append("manifest.json   <- which file holds which case, and why\n");
+        sb.append("_readable/<world>/   <- NBTJsonUtil renderings of the .dat files, for humans\n");
+        sb.append("manifest.json        <- which file holds which case, and why\n");
         sb.append("```\n\n");
-        sb.append("`customnpcs/` can be dropped straight into a save directory. `_readable/` is a\n");
-        sb.append("debugging aid: it is CustomNPC+'s own JSON rendering, which suffixes scalars\n");
-        sb.append("with their type (`5b`, `5L`, `1.0f`) and so is deliberately not strict JSON.\n\n");
+        sb.append("Each `<world>/` holds `customnpcs/` and nothing else, so it drops straight into\n");
+        sb.append("a save directory -- or, in Scribe, works as-is as a `cnpc_data_sets` overlay.\n");
+        sb.append("The readable renderings sit outside the world directories for that reason.\n\n");
+        sb.append("`_readable/` is a debugging aid, not a fixture: it is CustomNPC+'s own JSON\n");
+        sb.append("rendering, which suffixes scalars with their type (`5b`, `5L`, `1.0f`) and is\n");
+        sb.append("therefore deliberately not strict JSON. The widths being visible is the point.\n\n");
 
         sb.append("## The worlds\n\n");
         for (FixtureWorld world : worlds) {

src/fixtures/java/kamkeel/npcs/fixtures/WorldWriter.java

@@ -47,7 +47,10 @@ public final class WorldWriter {
         this.world = world;
         this.root = new File(outputRoot, world);
         this.customnpcs = new File(root, "customnpcs");
-        this.readable = new File(root, "_readable");
+        // Outside the world directory, not inside it. A generated <world>/ is meant to be usable
+        // as a drop-in overlay -- Scribe's smoke harness copies a set's contents straight into a
+        // server's world -- so it must contain customnpcs/ and nothing else.
+        this.readable = new File(new File(outputRoot, "_readable"), world);
         this.manifest = manifest;
         mkdirs(customnpcs);
         mkdirs(readable);