Switch from kingpin to cobra

This enables easier use of sub-commands for flexibility

cmd/root.go

@@ -0,0 +1,62 @@
+package cmd
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"runtime"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+// BuildInfo represents info collected as build-time.
+type BuildInfo struct {
+	Version string
+	Commit  string
+	Date    string
+}
+
+var rootCmd = &cobra.Command{
+	Use:           "rbheapleak",
+	Short:         "rbheapleak analyzes ObjectSpace dumps from Ruby processes.",
+	SilenceUsage:  true,
+	SilenceErrors: true,
+}
+
+func versionString(info *BuildInfo) string {
+	var buffer bytes.Buffer
+	var meta []string
+
+	buffer.WriteString(info.Version)
+
+	if info.Commit != "unknown" {
+		meta = append(meta, info.Commit)
+	}
+
+	meta = append(meta, runtime.Version())
+
+	if info.Date != "unknown" {
+		meta = append(meta, info.Date)
+	}
+
+	if len(meta) > 0 {
+		buffer.WriteString(fmt.Sprintf(" (%s)", strings.Join(meta, ", ")))
+	}
+
+	return buffer.String()
+}
+
+func Execute(info *BuildInfo) {
+	rootCmd.Version = versionString(info)
+	rootCmd.SetVersionTemplate("{{.Use}} {{.Version}}\n")
+
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}
+
+func init() {
+	rootCmd.Flags().BoolP("version", "v", false, "Show version.")
+}