Add SSL Valve to docs

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1568921 13f79535-47bb-0310-9956-ffa450edef68
Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56137
Explicitly use NIO connector in SSL example in server.xml so it doesn't break if APR is enabled.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1568926 13f79535-47bb-0310-9956-ffa450edef68