feat(fail-reporter-api): 'fail'-reporter no longer fails on mere warnings, but 'failOnWarning' does

- Consider a run successful if and only if there are no errors, regardless of warnings
- Have the fail reporter break the build if and only if there are errors, regardless of warnings
- Add a new `failOnWarning` reporter to fail on both warnings and errors, reproducing the
  previous behaviour of the `fail` reporter

BREAKING CHANGE: Set `file.success` to `true` and fail `fail`-reporter only when `file.errorCount`
is 0, even if `files.warningCount > 0`. To achieve the previous behavior of the `fail`-reporter you
may use the `failOnWarning`-reporter.
Merge pull request #19 from ejoubaud/default-fail-repoter-doesnt-fail-on-warnings

Stop failing on warnings by default
Slightly edited the commit message
chore(coffeelint-rules): use all new prefer english operator rule
chore(deps): update args-js and coffeelint-stylish
chore(release): prepare v0.4.0