Detect disallowed interface methods, docs update

Method calls from interface implementations are now detected (#212, @enumag wrote the test, thanks)

So you can disallow Interface::method() and Implementation::method() will also be detected. It already worked for constructors so makes sense to support it generally.

Attributes in config can be specified like #[\Foo()], not just like Foo (#207)

Make copy/pasting attribute names more straightforward. Similar already works for method calls etc.

Split the README into multiple smaller files (#209 + #210)

The README file was getting way too big already, making it shorter also gives better overview of what the extension does.

Internal changes

• Specify all required test files explicitly in given order and test all libs loaded (#213)
  And write a test to test that all test files are actually required because I don't trust anyone (=me) to not forget to add that file. Autoloading them seemed fine but the order could be more or less random which could break some tests, and it did.
• Use more precise list<type> instead of type[] where possible (#214)