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/map.go

@@ -0,0 +1,24 @@
+package commands
+
+import (
+	"log"
+
+	"github.com/spf13/cobra"
+)
+
+func NewMapCommand() *cobra.Command {
+
+	var mapCmd = &cobra.Command{
+		Use:   "map",
+		Short: "Display map information",
+		Long:  "Display map information",
+		Run: func(cmd *cobra.Command, args []string) {
+			err := cmd.Help()
+			if err != nil {
+				log.Fatal(err)
+			}
+		},
+	}
+
+	return mapCmd
+}