Support JavaBeans properties in addition to class fields

```
Gson uses class fields for conversion to/from Json. It would also be great
to have a mode of operation (using GsonBuilder) that forces Gson to use
methods as well. Essentially, a mode where Gson only considers the class
members with @Expose annotation.
```

Original issue reported on code.google.com by `inder123` on 27 Apr 2008 at 2:37
