Fixes to ssl/tls, misc improvements

* Use the PHP context options to configure tls rather than reinventing
  the wheel.
* Properly setup the SocketServer for ssl
* Added generic getter for config values

bin/mercureactd

@@ -56,8 +56,9 @@ if (isset($opts['C'])) {
         allow_origin: '*'
         csp: "default-src * 'self' http: 'unsafe-eval' 'unsafe-inline'; connect-src * 'self'"
       encryption:
-        cert: foo.pem
-        key: foo.key
+        local_cert: ~
+        local_pk: ~
+        passphrase: ~
 
     publish:
       overwrite_ids: false