In addition to building & testing AsyncDisplayKit, this new build script
can ensure that all example projects still compile. This will prevent
breaking API changes from landing without updating sample projects that
use them. It's also extensible, so we can add additional integration
tests in future (e.g., non-CocoaPods framework integration).
Don't consider the build broken if a feature branch is broken.
Move the actual build command to a separate script -- easier to read,
easier to maintain, and easier to run by hand.
