Added indigo compatibility and an additional raw detection publisher.

* Adapted CMakeLists to support builds on catkin+indigo.
* Created a new message AprilTagDetection with raw detection info.
* Created a new message AprilTagDetections for lists of detections.
* Publishing raw detections on /detections.
Merge pull request #4 from personalrobotics/indigo_fixes

Added indigo compatibility and an additional raw detection publisher.

I'm going to go ahead and merge this, as I have been using it stably for a month now.  If there are compatibility problems, let's open them as new issues.