add 'map' cli command to provide map information (#100)

* add 'map' cli command

- provides the following map information functions:
  - list all available maps in the global registry
  - display map metadata

- update docs with map command examples

* add list and info subcommands to map cli command

* rename map command list and info factory functions

* add --all flag to map info subcommand

* handle cmd.Help error

cli/commands/root.go

@@ -21,6 +21,12 @@ var rootCmd = &cobra.Command{
 func Execute() {
 	rootCmd.AddCommand(NewPlayCommand())
 
+	mapCommand := NewMapCommand()
+	mapCommand.AddCommand(NewMapListCommand())
+	mapCommand.AddCommand(NewMapInfoCommand())
+
+	rootCmd.AddCommand(mapCommand)
+
 	if err := rootCmd.Execute(); err != nil {
 		fmt.Println(err)
 		os.Exit(1)