fixes #6, refactor to use AnalysisError/Listener throughout dev_compiler

test/report_test.dart

Index: test/report_test.dart
diff --git a/test/report_test.dart b/test/report_test.dart
index f6f295d1a83893a94db0c4fc066372db9557af95..1d1d81e0f88febecc23090bf7bb7175b5a3dda5b 100644
--- a/test/report_test.dart
+++ b/test/report_test.dart
@@ -52,7 +52,7 @@ void main() {
 
       var mainMessage = mainLib.messages[1];
       expect(mainMessage.kind, "StaticTypeError");
-      expect(mainMessage.level, "severe");
+      expect(mainMessage.level, "error");
       expect(mainMessage.span.text, '"hi"');
       expect(
           mainMessage.span.context, '  x = /*severe:StaticTypeError*/"hi";\n');