Fix BoundingBox2D build issues (ros-perception#7)

* Fixing float definition on BoundingBox2D to build

* Cleaned up the comments for BoundingBox3D

msg/BoundingBox2D.msg

@@ -1,10 +1,13 @@
-# Note: This message *DOES NOT* plan to move to geometry_msgs in the final
-# implementation, because it uses pixels, not meters.
+# A 2D bounding box that can be rotated about its center.
+# All dimensions are in pixels, but represented using floating-point
+#   values to allow sub-pixel precision. If an exact pixel crop is required
+#   for a rotated bounding box, it can be calculated using Bresenham's line
+#   algorithm.
 
 # The 2D position (in pixels) and orientation of the bounding box center.
 geometry_msgs/Pose2D center
 
 # The size (in pixels) of the bounding box surrounding the object relative 
-# to the pose of its center
-float size_x
-float size_y
+# to the pose of its center.
+float64 size_x
+float64 size_y

msg/BoundingBox3D.msg

@@ -1,8 +1,9 @@
-# Note: This message plans to move to geometry_msgs in the final implementation.
+# A 3D bounding box that can be positioned and rotated about its center (6 DOF)
+# Dimensions of this box are in meters, and as such, it may be migrated to
+#   another package, such as geometry_msgs, in the future.
 
 # The 3D position and orientation of the bounding box center
 geometry_msgs/Pose center
 
-# The size of the bounding box surrounding the object relative to the pose of 
-# its center
+# The size of the bounding box, in meters, surrounding the object's center pose.
 geometry_msgs/Vector3 size