Removed minimalmodbus constants, added default constructor arguments

[limweichiang]

Removed unsupported module-level constants for BAUDRATE and TIMEOUT, instead using default arguments in the constructor to initialize the values for use on the pyserial object.

This change took effect as of MinimalModbus 1.0 which the RenogyRover class inherits, refer to https://minimalmodbus.readthedocs.io/en/stable/usage.html#default-values

Before fixing, the following error was encountered:

$ python3 renogy_rover.py 
Traceback (most recent call last):
  File "renogy_rover.py", line 185, in <module>
    print('Model: ', rover.model())
  File "renogy_rover.py", line 41, in model
    return self.read_string(12, number_of_registers=8)
  File "/home/ubuntu/.local/lib/python3.8/site-packages/minimalmodbus.py", line 751, in read_string
    return self._generic_command(
  File "/home/ubuntu/.local/lib/python3.8/site-packages/minimalmodbus.py", line 1170, in _generic_command
    payload_from_slave = self._perform_command(functioncode, payload_to_slave)
  File "/home/ubuntu/.local/lib/python3.8/site-packages/minimalmodbus.py", line 1240, in _perform_command
    response = self._communicate(request, number_of_bytes_to_read)
  File "/home/ubuntu/.local/lib/python3.8/site-packages/minimalmodbus.py", line 1406, in _communicate
    raise NoResponseError("No communication with the instrument (no answer)")
minimalmodbus.NoResponseError: No communication with the instrument (no answer)

[limweichiang]

Sorry for the messy PRs, I'm kinda getting used to collaborating on code using git, and should keep my branches cleaner. Please do review #9 first, as the fix there should precede this.

[corbinbs]

@limweichiang thanks for these adjustments as well!

Like with #9 , I'll combine all of these adjustments and give them some runtime against my own 40A Rover before releasing a new library version.

I'd love to set up some automated tests for PRs here in the future. If you ever come across any good charge controller simulators, I'd love to try to 📈 some test coverage of the library to help expedite releases and improve charge controller coverage.