Guess content type by the filename extension

[fogfish]

	var contentType string
	switch filepath.Ext(file) {
	case core.JPEG:
		contentType = "image/jpg"
	case core.JSON:
		contentType = "application/json"
	}

	return curl.stack.IO(ctx,
		http.PUT(
			ø.URI(string(url)),
			ø.ContentType.Set(contentType),
			ø.Send(buf),

			ƒ.Status.OK,
		),
	)

switch redundant the library shall be able to detect type automatically.