GitHub stats: Downloads across major versions

[bkimminich]

Currently all versions are counted individually, but only the last ~30 releases are actually considered. This leads to a very crowded chart:

The chart could be simplified by pre-processing the GitHub download data. Instead of counting all vX.Y.Z versions, they could be accumulated into just vX versions. This would - if additionally all downloads would be counted and not just the last 30 releases - lead to a very clean chart with lines only for v9, v10, v11, v12, v13, v14, and v15. In the available data set, the oldest version is v9.3.0, therefore all older versions do not occur.

Optionally an extra diagram could be added that shows the exact downloads per release (as today) but either limited to that last & months or to the last ~10 releases.

[bkimminich]