(modbus) Getting j2mod working, in principle
(modbus) Create a new modbus package

Will probably move it into its own sub-project later
(core) Get rid of IPv6 for now

I clearly didn't know how to represent it anyway, as it should be
8 groups of 16 bits!
(modbus) First stab at an actor makeing modbus requests
(modbus) WIP using a router to limit connections

Idea is to use a router to limit the number of concurrent connections to
a single gateway, and also set a suitable dispatcher(?) to handle the
fact that the actors necessarily block.
(modbus) Extend range of register addresses.

Actually, the correct range is that of an unsigned short.
(core) try out using the new actor
(modbus) Connect to the gateway lazily
(modbus) declare router's supervision strategy
(modbus) Define what a modbus measurement is.
(modbus) small tidying
(core) Fix small bug polling actor
(core) Playing with putting things together
(core) Cancel timeout when Result received.

Also cancel it when a Timeout itself is received in case the supervisor
decides to Resume this actor.
(core) Some additional logging
(modbus) WIP defining a directory for Modbus devices.

This looks like something that could be made common.
Merge branch 'feature-j2mod'