Add Allow and ExtendedStatus support to mod_status

I've extended the apache::mod::status class to accept an `$allow_from`
parameter similar to the existing apache::mod::info class, as well as
added an `$extended_status` parameter to control the ExtendedStatus
directive.

Added module docs and full testing support as well as updated the
README.md to indicate that the status class accepts additional
parameters.
Merge pull request #446 from dbeckham/mod_status_allow_rebase

Add Allow and ExtendedStatus support to mod_status (rebase of #419)