Modified apache module to support restricting Listen directive to specific IP addresses.

* New apache parameter 'listen_ips' takes an array of IP addresses
  for the Listen directive to use. Defaults to empty array, which
  will result in the standard "Listen 80" being used and Apache
  will bind to every IP address. This is the current behavior.
* This change also applies to the apache::mod::ssl module for
  handling SSL listeners.
* As a result the SSL configuration is changed from a static file
  to an ERB template. The template also updates the old module name
  to the dynamic "@name" variable, so all existing configurations
  will be updated. But since, apache::mod::ssl isn't linked into
  apache, this will not trigger an httpd service refresh.
Typo fix in README example.
Merge pull request #12 from ajz/master

Let Apache Listen Selectively