add signify

This is a port of the [signify(1)](http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man1/signify.1) utility from OpenBSD.
Yes, we have and you didn't add a test in the format that we like to have in our formulae. `make test` does a different thing to our `test do` block which ensures that there is a basic way of actually running the tool after it's been compiled and installed. `make test` does not handle the case where we fail to install, link or package the tool correctly causing it to segfault on startup. Look at `cmake.rb` and you may understand what we try to do with our tests.