Added FasterXML Jackson `ObjectMapper` based `HashMapper` implementation that allows flattening.
```java
class Person {
String firstname;
String lastname;
Address address;
}
class Address {
String city;
String country;
}
```
```bash
firstname:Jon
lastname:Snow
address:{ city : Castle Black, country : The North }
firstname:Jon
lastname:Snow
address.city:Castle Black
address.country:The North
```
Original pull request: #197.
568e41f8dd