Some more work on the graphs

Back in July I added some graphs that showed the last 150 days' worth of data. I wrote the code to generate them rather quickly and have not touched it since.

This evening I've made some changes to how they're generated (got rid of the user of gnuplot's smooth facility and have also added some labels) and I've also added two extra graphs: the wind chill and also the impact of wind chill (the latter being the temperature minus the wind chill).