Document added C API extensions from Lua 5.2/5.3.

doc/extensions.html

@@ -313,9 +313,13 @@ indexes for varargs.</li>
 C&nbsp;functions.</li>
 <li><tt>debug.upvalueid()</tt> and <tt>debug.upvaluejoin()</tt>.</li>
 <li>Lua/C API extensions:
+<tt>lua_version()</tt>
 <tt>lua_upvalueid()</tt>
 <tt>lua_upvaluejoin()</tt>
 <tt>lua_loadx()</tt>
+<tt>lua_copy()</tt>
+<tt>lua_tonumberx()</tt>
+<tt>lua_tointegerx()</tt>
 <tt>luaL_fileresult()</tt>
 <tt>luaL_execresult()</tt>
 <tt>luaL_loadfilex()</tt>
@@ -325,6 +329,8 @@ C&nbsp;functions.</li>
 <tt>luaL_pushmodule()</tt>
 <tt>luaL_newlibtable()</tt>
 <tt>luaL_newlib()</tt>
+<tt>luaL_testudata()</tt>
+<tt>luaL_setmetatable()</tt>
 </li>
 <li>Command line option <tt>-E</tt>.</li>
 <li>Command line checks <tt>__tostring</tt> for errors.</li>
@@ -370,6 +376,9 @@ LuaJIT supports some extensions from Lua&nbsp;5.3:
 <li><tt>io.read()</tt> and <tt>file:read()</tt> accept formats with or without a leading <tt>*</tt>.</li>
 <li><tt>table.move(a1, f, e, t [,a2])</tt>.</li>
 <li><tt>coroutine.isyieldable()</tt>.</li>
+<li>Lua/C API extensions:
+<tt>lua_isyieldable()</tt>
+</li>
 </ul>
 
 <h2 id="exceptions">C++ Exception Interoperability</h2>