Clarify C++11 styleguide wording around std::to_string.

styleguide/c++/c++11.html

Index: styleguide/c++/c++11.html
diff --git a/styleguide/c++/c++11.html b/styleguide/c++/c++11.html
index 123ecd8651ef92be7ba36289e6a8036ed026f0f4..168f53d61d0721eef42d1c83879dfc8f82556e2d 100644
--- a/styleguide/c++/c++11.html
+++ b/styleguide/c++/c++11.html
@@ -866,10 +866,10 @@ work in all our compilers yet.</p>
 </tr>
 
 <tr>
-<td>String to Number Functions</td>
+<td>String-Number Conversion Functions</td>
 <td><code>std::stoi()</code>, <code>std::stol()</code>, <code>std::stoul()</code>, <code>std::stoll</code>, <code>std::stoull()</code>, <code>std::stof()</code>, <code>std::stod()</code>, <code>std::stold()</code>, <code>std::to_string()</code></td>
-<td>Converts strings to numbers</td>
-<td><a href="http://en.cppreference.com/w/cpp/string/basic_string/stol">std::stoi, std::stol, std::stoll</a>, <a href="http://en.cppreference.com/w/cpp/string/basic_string/stoul">std::stoul, std::stoull</a>, <a href="http://en.cppreference.com/w/cpp/string/basic_string/stof">std::stof, std::stod, std::stold</a></td>
+<td>Converts strings to/from numbers</td>
+<td><a href="http://en.cppreference.com/w/cpp/string/basic_string/stol">std::stoi, std::stol, std::stoll</a>, <a href="http://en.cppreference.com/w/cpp/string/basic_string/stoul">std::stoul, std::stoull</a>, <a href="http://en.cppreference.com/w/cpp/string/basic_string/stof">std::stof, std::stod, std::stold</a>, <a href="http://en.cppreference.com/w/cpp/string/basic_string/to_string">std::to_string</a></td>
 <td></td>
 </tr>