-jar support and custom configuration

• Launch heapSpank using -jar syntax:
  java -jar heapSpank-0.6.jar 8173
• No support yet for a configuration file, so all config changes must be done via code. Just create a new class to extend DefaultConfig as shown here and pass in your subclass name with the -config parameter, like this:
  java -jar heapSpank-0.6.jar 8173 -config com.github.eostermueller.heapspank.leakyspank.console.FifteenSecondJMapHistoInterval