Complete rewrite.

Everything is done in the library now, Abema's go-mp4 lib no longer needed.

utils.go

@@ -0,0 +1,77 @@
+package mp4tag
+
+import ( 
+	"path/filepath"
+	"time"
+	"os"
+	"io"
+	"strings"
+	"fmt"
+)
+
+func containsRune(items []rune, value rune) bool {
+	for _, item := range items {
+		if item == value {
+			return true
+		}
+	}
+	return false
+}
+
+func containsOnlyNums(str string) bool {
+	for _, r := range str {
+		if !containsRune(numbers, r) {
+			return false
+		}
+	}
+	return true
+}
+
+func strArrToLower(arr []string) []string {
+	var lowerArr []string
+	for _, str := range arr {
+		lowerArr = append(lowerArr, strings.ToLower(str))
+	}
+	return lowerArr
+}
+
+func containsStr(arr []string, val string) bool {
+	for _, str := range arr {
+		if str == val {
+			return true
+		}
+	}
+	return false	
+}
+
+func getTempPath(path string) string {
+	fname := filepath.Base(path)
+	unix := time.Now().UnixMilli()
+	tempPath := filepath.Join(
+		os.TempDir(), fmt.Sprintf("%s_tmp_%d", fname, unix))
+	return tempPath
+}
+
+func getPos(f *os.File) (int64, error) {
+	return f.Seek(0, io.SeekCurrent)
+}
+
+func moveMP4(srcPath, destPath string) error {
+    inFile, err := os.Open(srcPath)
+    if err != nil {
+        return err
+    }
+    outFile, err := os.Create(destPath)
+    if err != nil {
+        inFile.Close()
+        return err
+    }
+    defer outFile.Close()
+    _, err = io.Copy(outFile, inFile)
+    if err != nil {
+        return err
+    }
+    inFile.Close()
+    err = os.Remove(srcPath)
+    return err
+}