v0.6.1

This release sets an upper bounds on the version of pymodbus, as there were breaking changes in v3.0.0. It also includes changes to handle the new changes, however these won't have any effect yet. I'll release a v0.6.2 once rpvelloso/Sungrow-Modbus#9 is merged, which fixes the same problem in a modbus4mqtt dependency and I can remove the pymodbus<3.0.0 restriction.