Migrate CLI parser from kingpin to kong

[chebread]

I suggest changing devd's CLI flag parser from alecthomas/kingpin to alecthomas/kong.

[wader]

Fine with me if it can be done without breaking CLI compatibility. Is there any part of the argument parsing that is tricky? routing? if so worth adding tests for kingpin that should pass with kong also?

[chebread]

Thanks. I'll take your feedback into account and prepare a PR for the Kong migration.