Ability to customize anchor names

[Andrey Somov]

The copy of the issue 102: https://code.google.com/p/snakeyaml/issues/detail?id=202

The idea is to provide a simple interface to be implemented by users:

public interface AnchorGenerator {

    String nextAnchor(Node node);
}

The original Java object is not available at this point but its Node representation can be used.

[Andrey Somov]

The proposal is ready to be reviewed: https://bitbucket.org/asomov/snakeyaml/commits/b5320ba15a9bb8611d61c2a8e5a112462321f517

1.17-SNAPSHOT can be used to test.

[Andrey Somov]

It will be delivered in version 1.17