Repl prints listy things with sugar

Searches for applications of "Nil" and "::" and prints them accordingly.
Print Nats as numerals

Might be more controversial than the list resugaring, since it's very
ad-hoc, but I can't be the only one sick of counting S's. :)
initial ideslave
minor cleanups
do IO in processInput rather than in process

This is a first step to use the process function for
the ideslave as well.
use process in ideslave loop
catch errors during receive and report them
make this a bit more useful, and use same protocol as emacs side :)