Revisit ROS message access through loops

[andrew103]

again, not 100% sure on how ROS creates its data objects, but this could potentially be reduced to:

joints = (attr for attr in dir(msg) if not attr.startswith('_'))
ja_bytes = []
for joint in joints:
  if getattr(msg, joint) // 256 > 0:
    ja_bytes.append(255)
    ja_bytes.append(getattr(msg, joint) % 255)
  else:
    ja_bytes.append(getattr(msg, joint))
    ja_bytes.append(0)

Originally posted by @agupta231 in #3 (comment)