Add initial non-multiarch Debian/Ubuntu packaging

This is the Debian/Ubuntu packaging for libsodium. It does not support multiarch because I don't know how to implement multiarch support (libsodium doesn't seem to be a trivial case to convert). Other than that it should be pretty proper; the binary revisions are properly declared and the library files are installed to /usr/lib.

I've created "packages" folder following the DNSCrypt convention. If that's not the correct way to do this, please let me know.