add version

Signed-off-by: jolheiser <john.olheiser@gmail.com>

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"flag"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -14,11 +15,24 @@ import (
 var Version = "develop"
 
 func main() {
-	if len(os.Args) < 2 {
+	fs := flag.NewFlagSet("isitup", flag.ExitOnError)
+	versionFlag := fs.Bool("version", false, "Display version and exit")
+	fs.BoolVar(versionFlag, "v", *versionFlag, "--version")
+	if err := fs.Parse(os.Args[1:]); err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	if *versionFlag {
+		fmt.Printf("isitup %s\n", Version)
+		return
+	}
+
+	if fs.NArg() < 1 {
 		fmt.Println("isitup requires a host to check")
 		return
 	}
-	host := os.Args[1]
+	host := fs.Arg(0)
 
 	r, err := Check(host)
 	if err != nil {