Improve kw-arg wrapper codegen

[samoconnor]

See: #28 where a stack overflow resulted from ambiguity in kw arg processing.

The logs(a...; b...) = logs(a..., b) needs to be replaced by something more predictable.

AWSCore.jl/src/Services.jl

Lines 1108 to 1123 in 8a74ec7

	function logs(aws::AWSConfig, operation, args=[])
	AWSCore.service_json(
	aws;
	service = "logs",
	version = "2014-03-28",
	json_version = "1.1",
	target = "Logs_20140328",
	operation = operation,
	args = args)
	end
	logs(operation, args=[]) =
	logs(default_aws_config(), operation, args)
	logs(a...; b...) = logs(a..., b)

See also JuliaLang/julia#26204