Release 0.8.0

Features:
- Add `servername` parameter to `apache` class
- Add `proxy_set` parameter to `apache::balancer` define

Bugfixes:
- Fix ordering for multiple `apache::balancer` clusters
- Fix symlinking for sites-available on Debian-based OSs
- Fix dependency ordering for recursive confdir management
- Fix `apache::mod::*` to notify the service on config change
- Documentation updates
Merge pull request #255 from hunner/release_0.8.0

Release 0.8.0