Add ansible vault support.

This also sets up a mechanism to pass in other ansible-related options
in a bang config file.  There is a new top-level attribute, ``ansible``,
with sample usage in ``examples/basic/just_run_a_playbook.yml``.
Update docs and version for 0.13
Add the bang.attributes submodules to docs
Add notes about installing RightScale dependencies
Return sorted host lists for ``bang --list``.

This addresses #11.
Fix handling of localhost in inventory
Add more examples to a_playbook.yml
Replace sphinxcontrib-programoutput with sphinx-argparse
Update stale documentation requirements
Add python-rightscale to devreqs.pip
Remove requirements.pip from travis-ci config

It is now included in the devreqs.pip.
Added S3 create_bucket
Propagate rs deployment and server name to ec2 tags.

Make sure ec2 instances are tagged with role=rs_server_name and
stack=rs_deployment_name.
Breaking change - Push rightscale inputs deeper in server config.

Prior to this change, one would specify the server template inputs in a
rightscale server config like this:

    servers:
      my_rs_server:
        # other server attributes omitted for brevity
        provider: rightscale
        inputs:
          DOMAIN: foo.net
          SOME_OTHER_INPUT: blah blah

Provider-specific attributes needed to create/launch servers will now be
nested one level deeper in an attribute named after the provider.  With
this new structure, the corresponding configuration for the example
above would look like this:

    servers:
      my_rs_server:
        # other server attributes omitted for brevity
        provider: rightscale
        rightscale:
          inputs:
            DOMAIN: foo.net
            SOME_OTHER_INPUT: blah blah
Add provider_extras to rightscale server consul.

This new argument to the define_server() and create_server() methods
allows any rightscale-specific server attributes in the bang stack
config file to pass through to the rightscale api call while allowing
all the intermediate Bang code to just ignore the attributes.
Add a doc and example for rightscale
Rephrase rightscale description in docs
Make provider_extras logic work for ServerDeployer.

This change allows passing provider-specific server launch arguments.
E.g. The following server config snippet assigns an IAM role to a server:

    servers:
      minimal:
        # other attributes omitted for brevity
        provider: aws
        aws:
          instance_profile_name: instance_profile_for_iam_role
Add example of a minimal server in AWS (including IAM role assignment).
Update version and release notes for 0.14