fix #18 - underscores break parsing

[tsheinen]

i changed the lexer match regex for identifiers from [a-zA-Z0-9\.]+ to [$\p{L}\p{Nl}_][0-9\p{L}\p{Nl}\p{Mn}\p{Mc}\p{Nd}_$.]* to more closely match the QML/JavaScript identifier rules.

I noticed that tests don't seem to pass even in a new clone of the repository. From a quick look at the comparisons it looks like a whitespace parsing issue, so it is probably caused by the whitespace commit a few back. I didn't modify the tests to try the expanded identifier set because they were all already pretty broken.