Fail build when there are YARD warnings.
Add travis folding and timing to build parts.

Inspired by https://github.com/vcr/vcr/commit/fa96819c92b783ec0c794f788183e170e4f684b2
Stop setting `-x`; it makes the build output too noisy.
Add 2.1.4 to travis build.
Split build functions into multiple files.
Merge pull request #85 from rspec/fail-build-on-yard-warnings

Fail build on yard warnings