We want to re-use the logic of the SendPaymentRequest code, most notably
the logic that prints the payment updates as a nicely formatted table to
the console, in other projects.
We want to export some of our CLI code to re-use in other projects. But
in Golang you cannot import code from a `main` package.
So we need to move the actual code into its own package and only have
the `func main()` in the `main` package.
