New strConcat concatenates strings in O(n) time.

* Accepts std::string and char const*.
* Also accepts numbers, bools and chars.
* New ripple::toString function augments std::to_string to handle
  bools and chars.

src/ripple_basics/utility/StringUtilities.cpp

@@ -412,14 +412,41 @@ public:
             "parseUrl: Mixed://domain/path path failed");
     }
 
+    void testStringConcat ()
+    {
+        testcase ("stringConcat");
+        auto result = stringConcat({});
+        expect(result == "", result);
+
+        result = stringConcat({"hello, ", std::string("world.")});
+        expect(result == "hello, world.", result);
+
+        result = stringConcat({"hello, ", 23});
+        expect(result == "hello, 23", result);
+
+        result = stringConcat({"hello, ", true});
+        expect(result == "hello, true", result);
+
+        result = stringConcat({"hello, ", 'x'});
+        expect(result == "hello, x", result);
+    }
+
+    void testToString ()
+    {
+        testcase ("toString");
+        auto result = toString("hello");
+        expect(result == "hello", result);
+    }
+
     void run ()
     {
         testParseUrl ();
-
         testUnHex ();
+        testStringConcat ();
+        testToString ();
     }
 };
 
-BEAST_DEFINE_TESTSUITE(StringUtilities,ripple_basics,ripple);
+BEAST_DEFINE_TESTSUITE(StringUtilities, ripple_basics, ripple);
 
 } // ripple