Extend functionality to work with pure enums (#6)

* Extend functionality to work with pure enums

* Code review changes

Altered `::values()` to act like `::names()` for backed enums, code style fixes, general cleanups

tests/Pest/ValuesTest.php

@@ -1,5 +1,9 @@
 <?php
 
-it('can return an array of case values')
+it('can return an array of case values from a backed enum')
     ->expect(Status::values())
     ->toBe([0, 1]);
+
+it('can return an array of case names from a pure enum')
+    ->expect(Role::values())
+    ->toBe(['ADMIN', 'GUEST']);