modbus plugin: Implement the "Dataset" config option.

modbus plugin: Implement the "Dataset" config option.

Hello Florian,

First of all, I would like to thank you for writing collectd. It is a
very nice and useful application!

Secondly, thanks for changing the license of the collectd modbus plugin.
I would like to eventually get it included in the package of collectd
that is shipped by debian and I hope the new license is acceptable to
them.

In addition, I think it would be nice to group a number of registers, to
make it easier to configure a number of identical devices. I wrote a
small patch (attached) that adds a config option 'Dataset', that works
like in the example below. The patch is only tested lightly. Could you
comment on the (preliminary) patch?

Signed-off-by: Florian Forster <octo@huhu.verplant.org>