Add documentation and examples for php version pragma.

Pragma version to specify versions for PHP5 and PHP7 extensions.
See issue #360.

Doc/Manual/Php.html

@@ -820,6 +820,15 @@ Results in the following in "example.php"
 echo "example.php execution\n";
 </pre></div>
 
+<p>
+The <b>version</b> pragma can be used to add version to generated PHP extension module. The version is inserted in the zend_module_entry block.
+</p>
+
+<div class="code"><pre>
+%module example
+%pragma(php) version="1.5"
+</pre></div>
+
 <p>
 The <b>include</b> pragma is a short cut to add include statements to
 the example.php file.