Extracted logic for obtaining status code

New method: `getStatusCode($error, $response)`
Extract methods

- Extracted logic for generating development error message to new
  method, `createDevelopmentErrorMessage($error)`.
- Extracted trigger logic to a new method, `triggerError($error,
  $request, $response)`.
CS fixes (trailing whitespace)
Merge branch 'hotfix/final-handler'

Improve `FinalHandler::handleError()`
Extracted createPipeHandlerCallback method

- from the pipe() method
CS fixes (trailing whitespace)
Merge branch 'hotfix/middleware-pipe'

Refactored `Middleware::pipe` by extracting methods for normalizing the path,
and creating a closure for object handlers implementing a `handle()` method.
Refactored `Next::__invoke()`

Extract methods:
- `resetSlash()`
- `resetPath()`
- `getBorder()`
- `stripRouteFromPath()`
Merge branch 'hotfix/next-invoke'

Refactors `Next::__invoke()` to extract methods and thus reduce length and
complexity.