Implement list command

pkg/cmd/list.go

+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	cli "github.com/spf13/cobra"
+
+	"github.com/tmrts/tmplt/pkg/tmplt"
+	"github.com/tmrts/tmplt/pkg/util/exit"
+	"github.com/tmrts/tmplt/pkg/util/validate"
+)
+
+var List = &cli.Command{
+	Use:   "list <template-path> <template-name>",
+	Short: "Lists templates found in the template registry",
+	Run: func(c *cli.Command, args []string) {
+		MustValidateArgs(args, []validate.Argument{})
+
+		d, err := os.Open(tmplt.Configuration.TemplateDirPath)
+		if err != nil {
+			exit.Error(fmt.Errorf("list: %s", err))
+		} else {
+			defer d.Close()
+		}
+
+		templateNames, err := d.Readdirnames(-1)
+		if err != nil {
+			exit.Error(fmt.Errorf("list: %s", err))
+		}
+
+		for _, name := range templateNames {
+			fmt.Println(name)
+		}
+	},
+}