gencert creates server + client certificates signed with the same self-issued CA

Usage of gencert:
  -client.cert string
	file to save client certificate (default "client-cert.pem")
  -client.key string
	file to save client certificate key (default "client-key.pem")
  -hosts string
	comma-separated list of hostnames
  -server.cert string
	file to save server certificate (default "server-cert.pem")
  -server.key string
	file to save server certificate key (default "server-key.pem")

Both client and server saved certificates are concatenated with CA certificate they were signed with. This CA can be used by either side to verify authenticity of certificate presented by other party.