added volume_id_in_tag option

As discussed in issue https://github.com/alestic/ec2-expire-snapshots/issues/7 I've added the feature that allows you to specify the volume-id in a tag vs. only using the value that's assigned at snapshot creation so that snapshots that are copied across regions can have a consistent expiration schedule.

One caveat is that this uses the [describe_tags] [1] method from the latest version of the Net::Amazon::EC2 module, 0.23. This module looks like it will be part of [saucy] [2], but since it isn't yet I've documented how I've built a .deb for it: http://blog.tonns.org/2013/07/building-perl-package-for-ubuntu.html 

  [1]: http://search.cpan.org/~mallen/Net-Amazon-EC2/lib/Net/Amazon/EC2.pm#describe_tags(%params)
  [2]: http://packages.ubuntu.com/source/saucy/libnet-amazon-ec2-perl