v0.18.0

Added

• AbstractInstantiation diagnostic to detect attempts to instantiate abstract classes via new ClassName().

Fixed

• Closure use() clause validation: now detects undefined variables referenced in closure use() clauses. Example: use ($i) will report UndefinedVariable if $i is not defined in the parent scope.
• Mixin method resolution with generics: docblock @mixin Foo<T> annotations now correctly resolve to class Foo instead of attempting to look up a non-existent class named Foo<T>.
• All 17 undefined_variable fixture tests now pass with correct line/column/message expectations.
• All 15 undefined_constant fixture tests now pass with correct line/column/message expectations.