Renaming ErrorHandler to ErrorHandlerMiddleware

[boesing]

As already mentioned in #190, there is a naming conflict in the ErrorHandler.

I had some feedback of trainees which asked me, why the ErrorHandler ain't a RequestHandler, as its name says.
That made me think about the naming and I realized, its just because of the missing Middleware postfix.

However, I'd like to rename the ErrorHandler to ErrorHandlerMiddleware to avoid future confusions about where the difference between RequestHandlerInterface and MiddlewareInterface is.

[boesing]

/cc @weierophinney @webimpress

[michalbundyra]

@boesing I think there might be some references to this class in the documentation so we need update it. Other than that LGTM 👍

[weierophinney]

This repository has been closed and moved to laminas/laminas-stratigility; a new issue has been opened at laminas/laminas-stratigility#2.

[weierophinney]

This repository has been moved to laminas/laminas-stratigility. If you feel that this patch is still relevant, please re-open against that repository, and reference this issue. To re-open, we suggest the following workflow:

• Squash all commits in your branch (git rebase -i origin/{branch})
• Make a note of all changed files (`git diff --name-only origin/{branch}...HEAD
• Run the laminas/laminas-migration tool on the code.
• Clone laminas/laminas-stratigility to another directory.
• Copy the files from the second bullet point to the clone of laminas/laminas-stratigility.
• In your clone of laminas/laminas-stratigility, commit the files, push to your fork, and open the new PR.
  We will be providing tooling via laminas/laminas-migration soon to help automate the process.