Limit merges to squashed?

[sean-parent]

Per CONTRIBUTING.md, we only want squashed merges. Should we update the settings to only allow squashed merges?

[dabrahams]

We decided a while back that we simply wanted to discourage “external” contributors from merging long series of semi-meaningless commits like this one, but that we wanted to reserve the right to curate a well-organized change-set (especially one where all commits pass tests) and merge it, so we didn't want to prevent merges. Everything is up for discussion, though.

[WalterSmuts]

especially one where all commits pass tests

Is this something we want to enforce? I believe we can tell CI to run the tests on each commit. Currently we only test the final commit of a merge.