Add CLI support and requirements file

[ray-yin]

Thanks for your script. I restructured the code and added CLI arguments to make it easier to use. The date/time inputs assume UTC time. I was going to add local timezone support, but that got more complicated than I expected. May still add it later but figured I'd share this first. I tested with Python 3.7.7 but it should work with any version of 3.x

Hope you find it useful.