Provide more useful output when class matchers fail

Currently the class-type matchers (`KWBeKindOfClassMatcher`, `KWBeMemberOfClassMatcher`, `KWBeSubclassOfClassMatcher`) only provide the type of class expected on failure:

```
[FAILED], expected subject to be kind of Foo
```

This actually makes the a test like `[[aFoo should] beKindOfClass:[Foo class]]` less useful than a test like `[[[aFoo class] should] equal:[Foo class]]` because the later will at least indicate what was received (`expected subject to equal Foo, got Bar`), providing a path forward.

This pull request extends the class matchers to output the class of the item received:

```
[FAILED], expected subject to be kind of Foo, got Bar
[FAILED], expected subject to be member of Foo, got Bar
[FAILED], expected subject to be subclass of Foo, got Bar
```