Roll Observatory packages and add a roll script

packages/petitparser/example/lispweb/lispweb.dart

+library petitparser.example.lispweb;
+
+import 'dart:html';
+import 'package:petitparser/lisp.dart';
+
+void inspector(Element element, Environment environment) {
+  var result = '';
+  while (environment != null) {
+    result = '$result<ul>';
+    for (var symbol in environment.keys) {
+      result = '$result<li><b>$symbol</b>: ${environment[symbol]}</li>';
+    }
+    result = '$result</ul>';
+    result = '$result<hr/>';
+    environment = environment.owner;
+  }
+  element.innerHtml = result;
+}
+
+void main() {
+  var root = new Environment();
+  var native = Natives.import(root);
+  var standard = Standard.import(native.create());
+  var environment = standard.create();
+
+  var input = querySelector('#input') as TextAreaElement;
+  var output = querySelector('#output') as TextAreaElement;
+
+  querySelector('#evaluate').onClick.listen((event) {
+    var result = evalString(lispParser, environment, input.value);
+    output.value = result.toString();
+    inspector(querySelector('#inspector'), environment);
+  });
+  inspector(querySelector('#inspector'), environment);
+}