At the moment Ansible prefers yes/no for module booleans, however booleans in playbooks are still using True/False, rather than yes/no. This changes modifies boolean uses in playbooks (and man pages) to favor yes/no rather than True/False.

This change includes:

- Adaptation of documentation and examples to favor yes/no
- Modification to manpage output to favor yes/no (the docsite output already favors yes/no)

implement lookup plugins for arbitrary enumeration over arbitrary things.   See the mailing list for some cool examples.

Adds a thirsty=yes|no to the get_url module, such that if downloading a large file from the internet you can decide
whether to download it every time or not -- will replace only on change, or decide to not download.  The default
is thirsty=no which will not download every time by default.

Adds the 'serial' keyword to a playbook which controls how many hosts can be running through a playbook at a single time.
The default is 0, which means all hosts.  If set to 1, each host would run a playbook all the way through before moving
on the next host.  Fact gathering is still parallel, regardless of the serial setting.