Showcase the new-style lookup plugin access in the authorized_key docs rather than the old-style $FILE

Showcase the new-style lookup plugin access in the authorized_key docs rather than the old-style $FILE

Three changes:
* Add set_default_selinux_context() to module_common that sets
  a file's context according to the defaults in the policy
* In atomic_replace(), set the default context for the file if
  selinux is enabled and the destination file does not exist.
* In authorized_key, set the default context when creating
  $HOME/.ssh and $HOME/.ssh/authorized_keys.  If these already
  exist, this won't touch them.

Signed-off-by: Brian Coca <briancoca+dev@gmail.com>

Fixes #1624.

This also adds module as an argument to keyfile().

 - added terse syntax to modules.rst
 - added description of special variables to template module

  plus a small fix in rst.j2 template
  manpages generated & checked
  modules.html generated & checked

whitespace + remove deprecated YAML parser (migration script lives in examples/scripts and warning was added
in 0.6 release)

Add encoding lines to python modules such that they can take unicode options if they are fed them, since the
AnsibleModule stuff no longer base64 encodes for simplicity and speed reasons.

Fixes ansible/ansible#522, no longer creates comment in ~/.ssh/authorized_keys, does not create directory or file if state==absent.

Fixes ansible/ansible#523. Removed 'with:' blocks so module works with Python 2.4 for CentOS 5 support, courtesy of mcodd/ansible@29af24b73222c97e30f5843b67e321b95fb6c979.