Migrates to CircleCI

[ashfurrow]

Fixes #117. CI times down to ~2 minutes. Anyone up for review?

[DivineDominion]

Have seen the comment in #117, am now pondering adding CI to other repos — is Circle just used less often for open source projects and thus builds faster, i.e. are we just buying a few months of cheap and fast builds, or is there any other advantage?

[ashfurrow]

That's an interesting question. I don't know how usage of the two compares, but Travis can be used by any repo, while the CircleCI macOS environments are still technically in beta and CircleCI asks you to contact them for free access for OSS repos (to make scaling more predictable maybe ?) whereas Travis doesn't have this extra step. That could make Circle a less common choice.

Both companies are great – I have friends at both of them. And they're both giving away free access to their very excellent infrastructure, helping our community grow in healthy ways. I saw our Travis macOS builds spending hours in queue (with the rest of the macOS OSS builds) to actually begin. That was having an impact on the developer experience in our community, so I looked into an alternative. I have nothing but respect and gratitude for both Circle and Travis.

Hope that clarifies things!