Feature request -- Output in JSON

[tubalainen]

Hello @strigeus !

Finally got things working! Thanks for the code.
My mistakes:

• Not entering the sender ID correctly, it does not say explicitly in the code "use only the last 6 digits, leave out the 400". Caused confusion for me and about one week troubleshooting.
• The frequency offset in hard to determine, I entered the value suggested in the screenshot and got a reading, adjusted based upon freq error presented.

Now, to parse more easily to an MQTT broker for use with any home automation tool, could you please add JSON output as an option? Thanks!

[JohanLeirnes]

Try changing line 183
from:
m += sprintf(m, "%5d: %7.1f W. %d.%.3d kWh. Batt %d%%. FreqErr: %.2f", seq, watt, pulse/1000, pulse%1000, battery, freq);

to:
m += sprintf(m, "{\"Sequence\":%5d,\"Watt\":%7.1f,\"kWh\":%d.%.3d,\"battery\":%d,\"FreqErr\":%.2f}", seq, watt, pulse/1000, pulse%1000, battery, freq);