Allow middleware to be easily extended
Allow middleware to be easily extended

- Marked `$stack` and `getUrlFromRequest()` as protected, to allow for
  extension.

liuggio/zend-stratigility,matwright/zend-stratigility,Maks3w/zend-stratigility,Diego-Brocanelli/zend-stratigility,xtreamwayz/zend-stratigility,phly/conduit,jguittard/zend-stratigility,codeliner/zend-stratigility,martinezdelariva/conduit