Star count challenge: keep pace with development

[smichel17]

Idle thought — it would be cool if there were a couple of star count goals like "number of closed issues on github" (currently 1829) and "number of commits" (currently 3810 on master). Maybe that's a bit nerdy (not sure what % of users will know what a commit is), but it would motivate me, I think, to "match" the development effort by @westnordost (and others).