Rhizome: Add query method.

We need an initial way to 'just get everything,' so provide a
basic implementation.

Author: Yong Bakos

lib/src/rhizome.dart

@@ -30,4 +30,11 @@ class Rhizome {
     _repertory.register(thing);
     return thing;
   }
+
+  /// WIP: Retrieve a list of [Thing]s meeting provided criteria.
+  /// WIP: Right now, omit the criteria and just return everything.
+  List<Thing> query() {
+    return _continuum.things.values.toList();
+  }
+ 
 }

test/rhizome_test.dart

@@ -51,5 +51,17 @@ void main() {
           repertory: Repertory(index: {information: uri}));
       expect(rhizome.store(information), equals(thing));
     });
+
+    test('WIP: #query of an empty Rhizome returns an empty list', () {
+      expect(rhizome.query().length, equals(0));
+    });
+
+    test('WIP: #query returns a list of every Thing', () {
+      final first = rhizome.store('Fake 1');
+      final second = rhizome.store('Fake 2');
+      expect(rhizome.query().length, equals(2));
+      expect(rhizome.query().contains(first), isTrue);
+      expect(rhizome.query().contains(second), isTrue);
+    });
   });
 }