How to run: In the index.html file, change "const svg = {insert the svg function to run}"
Where to find primitive components: the top of the <script> in the index.html file
Important design decisions: Rect x and y is the center of the rectangle and not the top left corner. This is to make switching from a rect to a circle/ellipse more convenient. Also, circle and ellipse use diameter instead of radius for the same reason.