Support for sub fiber's error handlers

[josebalius]

Please provide enough information so that others can review your pull request:

Closes #1438

It captures the mounted fiber's configured error handlers and of that fiber's subapps (it's recursive by nature). It is then searched by matching request path to prefix to find the best match. I figured there shouldn't be "that many" sub error handlers even in a large app, however, if this is the wrong assumption we will need a better data structure, something close to what the router does, to be honest. I opted to keep it simple and not over engineer it.

This is a submission for #hacktoberfest !

Explain the details for making this change. What existing problem does the pull request solve?

• Mounted fiber and its sub-apps error handlers are now saved in a new App.errorHandlers map
• New public App.ErrorHandler method that wraps the logic for which error handler to use on any given context
• Error handler match logic based on request path <=> prefix accuracy
• Typo fixes
• Tests

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[ReneWerner87]

thanks for the code

@josebalius can you add some documentation for the new feature in our documentation repository https://github.com/gofiber/docs

[josebalius]

@ReneWerner87 sure thing. Is https://github.com/gofiber/docs/blob/master/api/fiber.md the best place to add these docs? I am thinking of expanding on the ErrorHandler definition to mention that mounted fiber error handlers are retained by the top-level app and applied on prefix associated requests.

[ReneWerner87]

I am thinking of expanding on the ErrorHandler definition to mention that mounted fiber error handlers are retained by the top-level app and applied on prefix associated requests.

sounds good

[josebalius]

Here is docs PR: gofiber/docs#204

[josebalius]

@ReneWerner87 is there something else I should do to get these PRs merged?

[ReneWerner87]

No, its okay for now

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