Support stable PHP versions

[vitormattos]

For now, the matrix only stay accepting EOL PHP versions as we can see at the latest tag:

      matrix:
        php:
          - "5.3"
          - "5.4"
          - "5.5"
          - "5.6"
          - "7.0"
          - "7.1"
          - "7.2"
          - "7.3"
          - "7.4"
          - "8.0"

https://github.com/mikehaertl/php-pdftk/blob/0.13.1/.github/workflows/tests.yml#L8-L19

Suggestion:

• Make compatible with current supported PHP versions as expose at the official PHP website as 8.1 to 8.4
  • Bump dependencies
  • Update GitHub Actions
  • Implement linters and refactor tools like:
    • phpcs
    • psalm
    • rector
• Implement GitHub Actions to run linters

If I have the approve from maintainers, I can do this. But first, I have some questions to maintainers:

• Will be necessary to define ta minimum PHP version at composer.json. What minimum PHP version would you like to declare in composer.json, can I set as 8.1?
• Do you prefer to keep a legacy matrix or remove EOL versions entirely?

I think that would be best to set as 8.1 the minimum version.

[mikehaertl]

So far I always tried to support as many old PHP versions as possible (you never know which constraints some poor dev somewhere might hit...).

On the other hand the old releases are still around so I guess it's fine to move on.

As I'm not much into PHP development anyway lateley I guess your suggestions are fine.

[mikehaertl]

Merged.

Unless you want to add more improvments I'd create a 0.14.0 release now.

[vitormattos]

So far I always tried to support as many old PHP versions as possible (you never know which constraints some poor dev somewhere might hit...).

I like to support the most usual and what's necessary to solve my problems. Sometimes maintain support to an old version could generate a very big effort that don't pay my bills 😅

Unless you want to add more improvments I'd create a 0.14.0 release now.

I will like to implement more static analyses tools, sometimes this can help to solve issues that unit tests can't show. After this, I think that we can go ahead with a new release.

[mikehaertl]

I will like to implement more static analyses tools

Alright, then I'll wait with the release.

[vitormattos]

@mikehaertl I think that we can go ahead and create a new release maybe bumping the major version.

[mikehaertl]

Released 0.14.0. I think it would be weird to put out a 1.0.0 as I consider this little library to be mostly in maintenance mode now. Unfortunately I've missed the point where a 1.0.0 would have made more sense (many years ago).

Thanks for your contribution!