Restructure Changelog

Make "Changelog" the top level header, and move the existing headers one
level down.

CHANGELOG.md

@@ -1,12 +1,15 @@
+Changelog
+=========
+
 Version 2.0.0
-=============
+-------------
 
 - Fixed sslCert and sslPrivKey entries being ignored in the config.
 - Changed ssl key creation to be done at startup instead of on npm install.
 - Added error handling during master startup.
 
-Breaking Changes
-----------------
+### Breaking Changes
+
 - Node.js versions below 10 are no longer supported.
 - lib/authenticate no longer requires config to be passed to it.  Breaks
   playerManager.