Support of multiple modes.

[Krolken]

We might want to be able to support mutiple readout modes.

[emontnemery]

How about splitting out the specifics for each mode to subclasses of Iec6205621Client, the same way it's done for the transports?

[Krolken]

I am trying to move most of my communication libraries to a sans-io approach. So I would like to make a better distinction between the messages sent, the baudrate needed and the order the messages can be sent.

Mode A:

• Request Message - Expect an Identification Message
• Enter Programming mode - ACK, NACK, or EXIT
• Read, Write, EXIT - READ-response, Write-response, EXIT.

Mode B:

• Request Message - Expect an Identification Message - Then a DataMessage
• Enter Programming mode - ACK, NACK, or EXIT
• Read, Write, EXIT - READ-response, Write-response, EXIT.

Mode C

• Request Message - Expect an Identification Message

• AckWithDataReadout

• • Expect a DataMessage for readout

• AckWithProgrammingMode

• • Expect PasswordChallange
• • P1 or P2 password
• • ACK, NACK or EXIT
• • Read, Write, EXIT - READ-response, Write-response, EXIT.

• AckWithManufacturespecific

• • Leave it up to someone else to deal with that.

Mode D:

• Just listen to full readout. I am planning this feature for P1 port server.

Mode E:

• Needed for my DLMS library to move a meter to DLMS. But messages should be defined here for better reuse.