Added ability to output report to 'filePath' using 'intercept-stdout'

Because of issue #1, I was unable to use this plugin the way I wanted. By adding a script from [this gist|https://gist.github.com/benbuckman/2758563/] I added a snippet that highjacks `stdout.write()` and replaces it with `fs.writeFile()`, which allows the plugin to write to `filePath`. I also removed any of the XML parsing that was being done, because this method allows Mocha's reporters to do all the heavy lifting.

## Commit info
- Added 'intercept-stdout' gist from Ben Buckman
- Changed plugin to higjack stdout.write() before calling the mocha reporter
- This allows mocha's Reporter do all of the work, and this plugin just hijacks stdout.write() so that mocha's reporter automatically writes to the file named in 'filePath'
- Removed dependency on 'js2xmlparser' because mocha is already doing all the parsing we need