add GIF generator - #3

create_grid_gif.py renders the same poster once per snapshot year and stitches the frames into an animated GIF, using Overpass's date: (attic data) query to fetch OpenStreetMap's power-grid mapping as it existed at each point in time - handy for visualizing how a region's grid mapping has grown

Tested for Africa. Works well :)
africa_grid_paper_grid_timelapse