Update some modbus salve code and LICENSE file

[armink]

from https://github.com/cwalter-at/freemodbus

[pvyleta]

Perfect, thanks a lot! I really appreciate your effort.

One last thing: If possible, could you change the license for this gitHub repository so that it is clear this code is possible to be used under BSD? I think this would make life much easier to many developers, and also more people would consider your code for their projects.

https://github.com/armink/FreeModbus_Slave-Master-RTT-STM32/blob/master/LICENSE

[armink]

The LICENSE file is already changed. Please see
https://github.com/armink/FreeModbus_Slave-Master-RTT-STM32/pull/42/files#diff-9879d6db96fd29134fc802214163b95aR1

I will also explain the license on the readme.

[pvyleta]

OK, I did not realized that. I was using the link on main page of GitHub, and only wanted to ensure it will be changed as well:

[armink]

when this pr is merge the main page of GitHub will change