Update qm from 5.1.3 to 5.2.3

Update version number in documentation

Update README

6.9.4

Added QS-TX/RX to qpcpp library and examples

6.9.3

QP-Arduino 6.9.3

Release date: 2021-07-16
QP/C++  6.9.3
QP-nano 6.8.2
QM      5.1.2

6.9.2

Upgraded to QP/C++ 6.9.2 / Removed QP-nano

6.8.1

6.8.0

6.7.0

6.5.1