#112 Allow ant-style expansion of properties

Allow the ant-style expansion of properties in the configuration, e.g.:

foo=bar
wrapper.java.mainclass=com.mypackage.${foo}

Justification:

this would make configuration much easier, in particular when using the #include feature. Applications could easily use one java.properties file for all configuration and include that in the wrapper.conf file, without using the somewhat weird setFOO syntax.