add Havlak benchmark

```diff
+# Havlak benchmark: https://code.google.com/p/multi-language-bench/
+# Crystal Implementation
+
+# Intel i5 2.5GHz
+# c++: 28.8s 147Mb
+# java: 33.7s 909Mb
+# crystal: 35.1s 387Mb
+# go: 67.7s 456Mb 
+# scala: 66.8s 316Mb
```