For some reason, I believed that the source dir containing the main
program need to be named bin for dune to work smoothly. But actually,
it seems to work fine with src, so let's go for it.

with algo several actions, and allow lurette to chose them.

Also add the list of neighbors to the init function. The rationale is that
to give a sensible initial value to local vars of type 'Neighbor', we need
the neighbors number.

I could have chosen to pass an integer only. Well, who can the plus
can the minus.