Merge branch 'master' into export_responsewriter_app_engine

* master:
  Fixes bug when status code is negative
  Update README.md
  Updates CHANGELOG and AUTHORS
  Fixes html debug mode
  Using test mode
  Adds TestMode
  HTML template debug mode.
  Update README.md
  Typo in AUTHORS
  Adds debug mode (part 1)
  Updates AUTHORS.md
  Updates CHANGELOG
  Update README.md
Add gin.CreateContext(w, req) as a Test Helper