Adding reprojection error as an output to calibration

Also, bumping the threshold default to 2 pixels, since we're
using higher resolution images, and it generally fails with errors
close to 2 pixels (when it probably shouldn't)

Change-Id: I2bd84e7a6a48ed789ef6636e0892eed574459702
Signed-off-by: Jim Ostrowski <yimmy13@gmail.com>
diff --git a/frc971/vision/calibration.fbs b/frc971/vision/calibration.fbs
index 428fc83..64a5d3c 100644
--- a/frc971/vision/calibration.fbs
+++ b/frc971/vision/calibration.fbs
@@ -51,6 +51,9 @@
 
   // The camera number.  This may be empty, "0", or "1".
   camera_number:int (id: 8);
+
+  // The reprojection error associated with the camera calibration.
+  reprojection_error:float (id: 9);
 }
 
 // Calibration information for all the cameras we know about.