Add initial support for protocol mode B

[emontnemery]

This adds basic support for mode B:

• Add baudrate map for mode B
• Skip mode selection for standard readout

Accessing of programming mode is not implemented

[Krolken]

Thanks for starting support for Mode B.

But I would prefer a separate Client object over a mode selection arg.

So to have ModeCClient and ModeBClient

I think that would keep the code more maintainable and fixes for one type of meter would give less risk of breaking stuff for others.

Once A, D and E mode are implemented the code would othewise be filled with tons of if-statements making it hard to understand.

[emontnemery]

OK, that sounds good! Just to confirm, you mean refactoring by splitting out the specifics for each mode to subclasses of Iec6205621Client, which will then be an abstract class?

[Krolken]

I started a discussion about it for better collaboration. #22