Standardize headers and docstrings (#4417)

* Implement new headers

* Reformat 1

* Reformat 2

* Reformat 3 - math

* Reformat 4 - yaml

detect.py

@@ -1,4 +1,6 @@
-"""Run inference with a YOLOv5 model on images, videos, directories, streams
+# YOLOv5 🚀 by Ultralytics, GPL-3.0 license
+"""
+Run inference on images, videos, directories, streams, etc.
 
 Usage:
     $ python path/to/detect.py --source path/to/img.jpg --weights yolov5s.pt --img 640