Visual Package Structure in docs

[AlexEidt]

Updated the package_structure.md file to show a visual representation of all directories in the nba_api project.

[rsforbes]

This is awesome. We should figure out how to make this a part of the build to keep it always current.

[AlexEidt]

The script is located here: https://github.com/AlexEidt/Directory-Grapher.
It uses GraphViz for the visualization, however it can also use an online API (quickchart.io) to render the graph and then save to a file from the response. That way the GraphViz binaries won't need to be downloaded. Creating the graph should just be a matter of running that script on the nba_api directory from the outside as shown below.

dir.py // Script to create graph. Must be outside of project directory.
nba_api // Project folder.