Moved all messages to the messages/ folder.
This meant changing a lot of includes and things.
Fixed the encoders node.
Simplified the node to only advertise a single service - a query allows other nodes to find out, simply, the total distance traveled. The node also only handles plain encoder ticks, because distance and such computation should be done on the library end.
Added Encoders and USB/Serial ROS nodes. Some of the functions in thesrc/<node>.cpp files are not fully functional yet.