Implement new backend config system

This unifies the 3 methods of reading config

  * command line
  * environment variable
  * config file

And allows them all to be configured in all places.  This is done by
making the []fs.Option in the backend registration be the master
source of what the backend options are.

The backend changes are:

  * Use the new configmap.Mapper parameter
  * Use configstruct to parse it into an Options struct
  * Add all config to []fs.Option including defaults and help
  * Remove all uses of pflag
  * Remove all uses of config.FileGet

cmd/cryptdecode/cryptdecode.go

@@ -40,14 +40,14 @@ use it like this
 	Run: func(command *cobra.Command, args []string) {
 		cmd.CheckArgs(2, 11, command, args)
 		cmd.Run(false, false, command, func() error {
-			fsInfo, configName, _, err := fs.ParseRemote(args[0])
+			fsInfo, _, _, config, err := fs.ConfigFs(args[0])
 			if err != nil {
 				return err
 			}
 			if fsInfo.Name != "crypt" {
 				return errors.New("The remote needs to be of type \"crypt\"")
 			}
-			cipher, err := crypt.NewCipher(configName)
+			cipher, err := crypt.NewCipher(config)
 			if err != nil {
 				return err
 			}