x.509/Makefile-ca: Add a basic Makefile for creating self-signed CAs
x.509/Makefile-server: Add a basic Makefile for creating self-signed certs

This requires a local CA, which you can build using Makefile-ca.  Use
CA_KEY and CA_CERT to point at your local CA:

  $ make -f Makefile-ca
  $ make -f Makefile-server CA_KEY=key.pem CA_CERT=ca.pem
x.509/Makefile-stunnel: Add a basic Makefile for creating self-signed certs

This is similar to Makefile-server, but it only creates a single
key/certificate pair.  It also bundles the private key and certificate
together in stunnel.pem, which is the format the stunnel image expects
(mount it at the container's /etc/stunnel/stunnel.pem).
x.509/Makefile-link: Add a basic Makefile for linking wildcard certs