Add test model, shore up 'build' command more

test-projects/example.json

@@ -0,0 +1,27 @@
+{
+  "name": "foo",
+  "tree": {
+    "$className": "DataModel",
+    "ReplicatedStorage": {
+      "$className": "ReplicatedStorage",
+      "Rojo": {
+        "$className": "Folder",
+        "Plugin": {
+          "$path": "lib"
+        },
+        "Roact": {
+          "$path": "modules/roact/lib"
+        },
+        "Rodux": {
+          "$path": "modules/rodux/lib"
+        },
+        "RoactRodux": {
+          "$path": "modules/roact-rodux/lib"
+        },
+        "Promise": {
+          "$path": "modules/promise/lib"
+        }
+      }
+    }
+  }
+}