Fix documentation exemple. If http_port is explicitly set to an empty
string, tomcat server.xml is generated with something like :

    <!-- See conf/connector-http--instancename.xml for this connector's
    config. -->
    &connector-http--instancename;

The -- inside the comment make tomcat fail with :

org.xml.sax.SAXParseException; systemId: file:///srv/tomcat/instancename/conf/server.xml; lineNumber: 59;
columnNumber: 35; The string "--" is not permitted within comments.
replace double quotes with simple when possible, it will avoid puppet-lint to raise errors when exemples are c/p
Merge pull request #53 from maxenced/dont-specify-empty-http-port

A few README.md changes