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 was trying to write a log parser for a high traffic app. Throwing exception can have significant performance impact.

Yes, it's an orthogonal feature. Sorry I forgot to mention it.