Add duplicate telegram check. about wmbusmeters HOT 1 CLOSED

I have pushed to master support for --ignoreduplicates (for the commandline) ignoreduplicates=true
for the conf file. This will use a memory of the last 10 telegrams and ignore any duplicates within
that memory.

Duplicates arrive if you have multiple dongles connected to wmbusmeters.
Either for experimentation or because you have one really long usb cable
to one dongle to capture certain meters better. Sometimes however
the same telegram will be received by both dongles, if you have supplied --ignoreduplicates
then the most recently received will be silently dropped (drop is visible if --verbose is enabled.)

Why is it not enabled by default? Because if you are experimenting with different dongles
and antennas, the json now contains for example:
device="im871a[12345678]" rssi_dbm=-53

This way you can have multiple dongles connected and monitor their rssi levels and
whether they receive a telegram at all.

Most users only have a single dongle anyway.

Unfortunately the current memory is a simple sha256 hash of the exact telegram bytes.
When a telegram is repeated by a repeater, then it might get modified on the DLL level
and/or a middle layer inserted to show that it has been repeated.
The current code does not detect this and will report a direct telegram as distinct
from such a repeated telegram.

When someone actually starts receiving repeated telegrams and direct telegrams,
then they will have to send me examples of how the repeated telegrams look.
I cannot write code for something that I am not sure what it looks like. :-)

from wmbusmeters.