Major changes for static analysis and testing purposes.

Some breaking changes:

* $pass is removed
* Classes are final

Make CI happy with platform constraints

Clarify license and update deps

Clarify license

Support callables

Add generics to exceptions (for static type checking tools)

PHP 7.3+ is now a requirement for the library

Drop phpdoc template parameter as it cannot be not used

Latest Psalm features (with more type coverage)

Psalm docblock support, and removed From class replaced with methods …

…on an abstract base class.