Add Debian packaging

This adds Debian packaging files for siegfried. It contains a complete `debian` directory except for the changelog, which references specific OS releases. (I'm maintaining one for Ubuntu 12.04 and 14.04, but I imagine hypothetical packagers for other Debian distros would want to maintain their own.)

This *should* be compatible with any Debian-based distro which includes go 1.2+ and the dh-golang buildscripts.

The packaging here contains one patch, which configures `sf` to look for PRONOM data in `/usr/share/pronom` instead of the user's home directory; the data included in the tarball is installed there. I'm planning to bump siegfried's revision as new PRONOM releases come out, but users should also be able to upgrade their own PRONOM data with `sudo sf -update`.

This depends on separately-packaged copies of the msoleps, mscfb and match repos; I'm submitting pull requests for their packaging too.