[API] Added a `CapturedLogger` module to capture $stdout/$stderr with the "CI::Reporter" gem

When running the YAML tests, hook into the `Logger#info|debug|...` etc methods
and call `$stderr.puts`, so it's properly captured by the <https://github.com/nicksieger/ci_reporter> gem.

See: https://github.com/nicksieger/ci_reporter/blob/master/lib/ci/reporter/test_suite.rb#L43-L51