Surefire (JUnit) formatter

Hi,

just wanted to send you a PR for a first pass at a Surefire formatter that I've implemented. It doesn't support timings or errors at the moment (as per the de facto spec that you'd linked to on your issue tracker), as I wasn't sure how to parse that info from the results object without further investigation.

But said I'd submit it to you to get initial feedback before trying to get it 100%.

The change I made to core/phantomas.js was to allow the formatted output to be saved to a file on its own — my use case was to make the generated file available to Bamboo, so that it could parse test results & the logger seemed to be adding in general debug information too, so I created a second logger just for the results file. Possibly this isn't needed if I get the flags (silent, etc) right?


Great work on Phantomas! Looking forward to getting it properly implemented on my project. 
Would appreciate any feedback on the PR.

Cheers
Dave