build(platform): Improve consistency (yarn), and async

[bfricka]

• Add CircleCI override to use latest yarn for deterministic builds
• Refactor some overly obtuse functions
• Use async throughout
• Add commitizen-friendly badge

[coveralls]

Coverage remained the same at 88.563% when pulling 8be24cf on bfricka:dev/build-improvements-2 into 8804156 on ngrx:master.

[bfricka]

Couple things about this PR:

1. Using [email protected] because several earlier versions have a regression that causes issues symlinking to ./node_modules/.bin. See this issue.

2. The biggest improvement is using yarn instead of npm. This improves perf a bit, but much more importantly, it gives build determinism.

3. This doesn't improve build perf like the last one. The async stuff is just for consistency, and likely wouldn't have a demonstrable impact unless the numbers of blocking tasks got significantly higher. That said, it's probably a good idea for io stuff to be async anyways, if only because most of it already was anyways.

I was actually planning for this PR to be unit tests, but with the latest commits (lots of new deps), I ended up running into the aforementioned symlink bug with my version of yarn, and couldn't get the project to build. So I went down the rabbit hole, ended up tweaking a few things, and here we are.

[coveralls]

Coverage remained the same at 88.563% when pulling e403aca on bfricka:dev/build-improvements-2 into 8804156 on ngrx:master.

[bfricka]

One more thing: We should probably update contributing, to refer to yarn. Until npm@5 becomes more mainstream, the only way for determinism is something like shrinkpack, but since this repo is already using yarn, it seems reasonable to consider standardizing on that.

[MikeRyanDev]

Thank you! These build-related PRs are very welcome.

[MikeRyanDev]

Regarding the contributing doc, I'll gladly accept a PR updating it.