The config command group manages the config file:
config init - write default config (moved from top-level init)
config edit - open the config in $EDITOR (falls back to vi)
config get - print a value by dotted YAML path (s3.bucket)
config set - set a scalar value by dotted YAML path
get/set operate on the yaml.Node tree so comments and formatting in
the config file are preserved across edits. set creates intermediate
maps as needed.