Add support for network events in Listen 2.5

Add the -o option to specify the address to listen to for network
events. This uses the network event functionality of Listen 2.5 and is
particularly useful in VM (e.g. Vagrant) that don't support native file
events.
Require Listen ~>2.5
Updated to use the listen script now in listen 2.6
Merge pull request #555 from ideasasylum/master

Add support for network events in Listen 2.5