Parser now correctly reverses the sign of the timezone offset

* Parser now correctly reverses the sign of the timezone offset, per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset
* Test for the above
* .gitignore file, so folks don't commit node_modules

I encountered this issue when I first tried to use clf-parser and wondered why all the date objects were eight hours off.

Thanks for clf-parser!