Make IO.write() call toString on its argument.

corelib.wren

@@ -0,0 +1,23 @@
+// Note: This is converted to a C string literal and inserted into
+// src/wren_core.c using make_corelib.
+class IO {
+  static write(obj) {
+    IO.write__native__(obj.toString)
+    return obj
+  }
+}
+
+class List {
+  toString {
+    var result = "["
+    var i = 0
+    // TODO: Use for loop.
+    while (i < this.count) {
+      if (i > 0) result = result + ", "
+      result = result + this[i].toString
+      i = i + 1
+    }
+    result = result + "]"
+    return result
+  }
+}