Updated `.gitignore` so git always show when I need to remove the `xbomb` binary
Added upstream PGP signing key
Made `debian/watch` look for upstream signatures
Made `debian/source/include-binaries` recognize the upstream signing key
Moved `debian/upstream-signing-key.pgp` to `debian/upstrea/signing-key.asc`

According to the instructions on the `debian/watch` wiki:
https://wiki.debian.org/debian/watch/#Cryptographic_signature_verification
Updated `debian/source/include-binaries
Updated `debian/changelog` with most recent changes