formatter package heavy refactoring

- make it possible to extract the formatter implementation from the
  "common" code, that way, the formatter package stays small
- extract some formatter into their own packages

This is essentially moving the "formatter" implementation of each type
in their respective packages. The *main* reason to do that, is to be
able to depend on `cli/command/formatter` without depending of the
implementation detail of the formatter. As of now, depending on
`cli/command/formatter` means we depend on `docker/docker/api/types`,
`docker/licensing`, … — that should not be the case. `formatter`
should hold the common code (or helpers) to easily create formatter,
not all formatter implementations.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

cli/command/container/diff.go

@@ -41,7 +41,7 @@ func runDiff(dockerCli command.Cli, opts *diffOptions) error {
 	}
 	diffCtx := formatter.Context{
 		Output: dockerCli.Out(),
-		Format: formatter.NewDiffFormat("{{.Type}} {{.Path}}"),
+		Format: NewDiffFormat("{{.Type}} {{.Path}}"),
 	}
-	return formatter.DiffWrite(diffCtx, changes)
+	return DiffFormatWrite(diffCtx, changes)
 }