Better support typed properties

Upgrades the underlying squirrelphp/strings component. This
removes compatibility to diverging property paths defined
in the form, we now only support direct properties which are
mapped 1:1 in the form.

Note that if filter annotations are used without direct mappings,
this might lead to errors and/or not work anymore.

The PHP 8 support is preliminary, as it was not tested yet.

v0.8.6

Relax PHP version constraint

v0.8.5

Add RemoveHTMLTagCharacters filter

v0.8.4: Make library PHP 7.4+ only

- Use new functionality as far as possible
- Improve project configuration

v0.8.3

Allow Symfony 5 and switch to composer-bin-plugin

v0.8.2: Add string tester integration

No selector yet, just make the first two testers
available through the bundle / dependency injection.

v0.8: Adjust to changes in strings component

Also start with a proper documentation, although it is still
incomplete.

v0.7.1

Add new filters from v0.7.1

First official release

Building on top of squirrelphp/string v0.7