Standardize headers and docstrings (#4417)

* Implement new headers

* Reformat 1

* Reformat 2

* Reformat 3 - math

* Reformat 4 - yaml

train.py

@@ -1,4 +1,6 @@
-"""Train a YOLOv5 model on a custom dataset
+# YOLOv5 🚀 by Ultralytics, GPL-3.0 license
+"""
+Train a YOLOv5 model on a custom dataset
 
 Usage:
     $ python path/to/train.py --data coco128.yaml --weights yolov5s.pt --img 640
@@ -6,6 +8,7 @@ Usage:
 
 import argparse
 import logging
+import math
 import os
 import random
 import sys
@@ -13,7 +16,6 @@ import time
 from copy import deepcopy
 from pathlib import Path
 
-import math
 import numpy as np
 import torch
 import torch.distributed as dist