Deprecate the mirror matchers library (flutter#131)

I cannot find usage. Asserting that an object has a property with a
known name can be accomplished by casting to `dynamic` and attempting to
read from that property. Asserting that an object has a property with a
name that is unknown at compile time has no known use case, if it comes
up it would re rare enough that the code for using mirrors to solve it
can be put into the test.

CHANGELOG.md

@@ -1,5 +1,6 @@
-## 0.12.7-dev
+## 0.12.7
 
+- Deprecate the `mirror_matchers.dart` library.
 - Update minimum Dart SDK to `2.4.0`.
 
 ## 0.12.6

lib/mirror_matchers.dart

@@ -2,6 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+@deprecated
+library mirror_matchers;
+
 /// The mirror matchers library provides some additional matchers that
 /// make use of `dart:mirrors`.
 import 'dart:mirrors';

pubspec.yaml

@@ -1,5 +1,5 @@
 name: matcher
-version: 0.12.7-dev
+version: 0.12.7
 
 description: >-
   Support for specifying test expectations via an extensible Matcher class.

test/mirror_matchers_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// ignore_for_file: deprecated_member_use_from_same_package
+
 @TestOn('vm')
 
 import 'package:matcher/mirror_matchers.dart';