Refactor follow-up

[tofu-rocketry]

#149 isn't the prettiest.

• It would be neater to construct and pass around a dictionary of Ssm2 parameters (though the config parser and log could still be separate arguments.
• A single function to invoke a sender/receiver would be useful rather than having call 3 separate functions in the main program.
• Further splitting up of the functions and adding unit testing.