Nodelets for zero-copy message passing between nodes

[digikar99]

http://wiki.ros.org/nodelet

It'd be great to have this for, say, publishing images from a sensor at higher rates.

From #4:

Me: Is this the same as nodelets - seems so to me; should I open a separate issue if not?

@Gaya: nodelets is not just for "running multiple ROS nodes in different threads in one process", which this issue is about. Nodelets also allow for efficient message passing between the different nodes of the same process. If you want efficient zero-copy message passing, open a new issue. If you only care about running multiple nodes in one REPL image, this issue is all you need.

...I personally am not going to put effort into implementing this. When I need multiple lisp nodes in my system, I just compile myself an executable (with add_lisp_executable) and run it in a terminal, in addition to my REPL image. One can also start two *inferior-lisp* processes in Emacs and have the other node run there. I've done that too, works pretty well. My lisp nodes usually publish with very low frequency, so I never bothered with the efficient message passing.

Okay, thanks for the clarification! I'm fairly new to ROS, but I'll look in a month or two after some of my other tasks if this is something I can give an attempt and issue a PR.