Standardize headers and docstrings (#4417)

* Implement new headers

* Reformat 1

* Reformat 2

* Reformat 3 - math

* Reformat 4 - yaml

utils/metrics.py

@@ -1,9 +1,12 @@
-# Model validation metrics
+# YOLOv5 🚀 by Ultralytics, GPL-3.0 license
+"""
+Model validation metrics
+"""
 
+import math
 import warnings
 from pathlib import Path
 
-import math
 import matplotlib.pyplot as plt
 import numpy as np
 import torch