Upgrade dependencies + require PHP 8.1

Otherwise no new or changed functionality.

First stable release

The purpose of this library should be quite established by now. The documentation could still be better, but it should be adequate for the start.

Add new Filter

Add RemoveNonAlphabeticFilter

Bump dependency for debug

Switch to squirrelphp/debug 2.x and refactor attribute. Should release this as v1.0 soon, but the documentation first has to be amended.

v0.10.3

Add regex wrapper

Documentation update + PHP 8.1 changes

• Add documentation for string testers
• Avoid strlen null deprecation message because a variable
  was not propery type checked
• Upgrade quality tools

Initialize model via reflection instead of new

Mandatory arguments lead to type errors so far because
the string filter extension tried to create a new class
via new instead of via reflection. Now with reflection
we ignore uninitialized properties of the class in our
string filter processor to be less error-prone.

Set PHP8 as minimum version

• Rename Annotation directory to Attribute (BC break)
• Check tests with Psalm
• Remove doctrine annotations dependency & support

Add streamline email filter

This will lowercase the domain part but keep the username part of the email case-sensitive, as defined by the current RFCs. This way duplicates because of domain part casings can be avoided.

v0.9.2: Make $names in attribute public

There were some problems with Symfony var-exporter when using
forms. Actual cause is unclear, but setting $names to public
fixes the issue and has no other ramifications.