Created by: dulmandakh
this PR is trying to add Circle CI support. I found that RN and Fresco use Circle CI, but also many open source projects.
It builds BUCK in 5 minutes (https://circleci.com/gh/dulmandakh/buck/101), while Travis CI in 14 minutes (https://travis-ci.org/facebook/buck/jobs/453861250). Also we can reduce time by utilizing workspace shared data.
FYI, I'm on free plan and it has limited resources, which might be causing weird failures, and taking more time to build.