Remove irrelevant/wrong check for 0

This fixes #16

Add checksum validation for received sensor data

Cleanup, restructure, refactor to C++11

* Cleanup and restructure code and add clang-format

* Further improve code and reduce sketch size

* Address review comments

* Add comment for bit-shift operation

* Fix parseState not returning which causes inf loop

- Cleanup some other code

* Address review comments

* Remove clang-format

* formatting

* formatting

* bump firmware version

Co-authored-by: Sören Beye <github@hypfer.de>

Fix #3