Provide a parse tree view to solve issue #12

Add a `tryParseTree()` method to `Parser`. The code has been tested against a relatively complex project of mine. The result is satisfactory to me. You can review the test cases to see the result.
I remember we discussed the issue a while ago... given the current state (dead?) of codehaus, what we can do is simply change the license of jparsec to a simple and classical Apache 2 License with shared copyright: Each contributor retains copyright on its contributions. Not sure about the legalese stuff, but I can check on what Apache requires and simply do the same.