Convert filet to support parallel execution

[jovandeginste]

We create a new list of files per TestReporter. This needed a map, and thus some helper functions to help with locking around the map.

This however changes the way you can access the Files array. You now need to access it through the map key (see the README changes)

Fixed #5

Signed-off-by: Jo Vandeginste [email protected]

[jakesylvestre]

This would be awesome!