feat: set up FFI

Signed-off-by: Sphericalkat <me@kat.bio>

example/readability_example.dart

@@ -0,0 +1,7 @@
+import 'package:readability/readability.dart';
+
+void main() {
+  var parser = ReadabilityParser();
+  Article article = parser.parse('https://www.bbc.com/sport/football/articles/cl7y4z82z2do');
+  print(article.toString());
+}