make cpp link relative

Author: psifertex

sphinx_rtd/layout.html

@@ -174,7 +174,7 @@
           {%- endif %}
 
           {%- include "searchbox.html" %}
-	  <div class="cpplink"><a href="https://api.binary.ninja/cpp/">C++ Documentation</a></div>
+	  <div class="cpplink"><a href="./cpp/index.html">C++ Documentation</a></div>
 
           {%- endblock %}
         </div>