Move from json-string based transfer between client and host to C struct / class based transfer

This change allows sending up to 6 sensor measurements with one ESPNow send call.

mentioned in issue #41 (closed)

mentioned in issue #46 (closed)

added 1 commit

• 8f675f68 - Getting Ack-Response time down to <15ms

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added 1 commit

• 65e20270 - Minor cleanup

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merged