feat(reporter): Introduce error reporter.

Small helper class to store errors and create helpful error messages.
style(spec): Remove ddescribe.

I really need a commit hook for this.
feat(parser): Use Reporter for failures.
Merge branch 'ErrorReporter'

* ErrorReporter:
  feat(parser): Use Reporter for failures.
  style(spec): Remove ddescribe.
  feat(reporter): Introduce error reporter.