add util::crop_utf8 (stringutil)

test/util/stringutil.cpp

@@ -0,0 +1,10 @@
+#include "util/stringutil.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(stringutil, crop_utf8) {
+    // Project source files must be UTF-8 encoded
+    std::string str = "пример";
+    str = str.substr(0, util::crop_utf8(str, 7));
+    EXPECT_EQ(str, "при");
+}