Downsample graphs that have too many stars

[David Tolnay]

For example in https://gistpreview.github.io/?9b4088406b4c2bb82beb6ec1b388c7ac there are so many stars that I ran sed '/:[0-9]*[^0]\},$/d' to strip out all but every 10th one, cutting the file down to 1/10th the size and improving ui responsiveness.

This should be done automatically to limit the number of data points per repo, or perhaps there should be some flag to control the downsampling.