[config] first cut of config rewritten in golang

still to do:
* Rework disk format to be okay with quotes
* Fix Dockerfile deployments
* Dedup code in the subcommands
* Add --encode
* Add deploytests for the new stuff
* Restore some log messages (should I make some helpers in common?)
* Restore some functions that may be used by 3d-party plugins

plugins/config/src/commands/commands.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	common "github.com/dokku/dokku/plugins/common"
+	configenv "github.com/dokku/dokku/plugins/config/src/configenv"
+	columnize "github.com/ryanuber/columnize"
+)
+
+const (
+	helpHeader = `Usage: dokku config [<app>|--global]
+
+Display all global or app-specific config vars
+
+Additional commands:`
+
+	helpContent = `
+    config:get (<app>|--global) KEY, Display a global or app-specific config value
+    config:set (<app>|--global) [--no-restart] KEY1=VALUE1 [KEY2=VALUE2 ...], Set one or more config vars
+    config:unset (<app>|--global) KEY1 [KEY2 ...], Unset one or more config vars
+	config:export (<app>|--global) [--envfile], Export a global or app environment
+`
+)
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+
+	cmd := flag.Arg(0)
+	switch cmd {
+	case "config":
+		target := flag.Arg(1)
+		env, err := configenv.NewFromTarget(target)
+		if err != nil {
+			common.LogFail(err.Error())
+		} else {
+			fmt.Println(env.String())
+		}
+	case "config:help":
+		usage()
+	case "help":
+		fmt.Print(helpContent)
+	default:
+		dokkuNotImplementExitCode, err := strconv.Atoi(os.Getenv("DOKKU_NOT_IMPLEMENTED_EXIT"))
+		if err != nil {
+			fmt.Println("failed to retrieve DOKKU_NOT_IMPLEMENTED_EXIT environment variable")
+			dokkuNotImplementExitCode = 10
+		}
+		os.Exit(dokkuNotImplementExitCode)
+	}
+}
+
+func usage() {
+	config := columnize.DefaultConfig()
+	config.Delim = ","
+	config.Prefix = "\t"
+	config.Empty = ""
+	content := strings.Split(helpContent, "\n")[1:]
+	fmt.Println(helpHeader)
+	fmt.Println(columnize.Format(content, config))
+}