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

This is a rebase of 555e0f7 submitted in #419 against the most recent mod_status changes.  I also added class docs and cleaned up the testing a bit as well as added a couple of extra test cases.  `rake spec` finishes cleanly.

***Commit Message:***

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.