add benchmarks for String

test/Benchmark/app/benchmark/string/include.rb

@@ -0,0 +1,25 @@
+def string_include(x)
+  x.report "include? with ASCII match" do
+    100000.times do
+      $short_sentence_ascii.include?("Candahar")
+    end
+  end
+
+  x.report "include? with ASCII nomatch" do
+    100000.times do
+      $short_sentence_ascii.include?("abcde")
+    end
+  end
+
+  x.report "include? with UTF8 match" do
+    100000.times do
+      $short_sentence_utf8.include?("ロンドン")
+    end
+  end
+
+  x.report "include? with UTF8 nomatch" do
+    100000.times do
+      $short_sentence_utf8.include?("日本")
+    end
+  end
+end