Move 'net/ipv6/6to4.yml' playbook

Playbooks will be sorted to more subdirectories as the need arises.
Add 'tools/hostname.yml' playbook

This playbook can be used to change hostname and FQDN of a host to be
the same as the one defined in Ansible inventory.
Update CHANGELOG.rst
Merge pull request #51 from drybjed/playbook-updates

New playbook, updated changelog