Add stub for PhpStorm IDE autocompletion and code inspection

[cboulanger]

Currently, the PhpStorm IDE cannot deal with PHP Yaz functions, doesn't autocomplete them and marks them as "unknown". Providing a simple stub could change that:

https://github.com/jetbrains/phpstorm-stubs

If you have one, it would be great if you'd submit it there, otherwise I might find some time to stitch it together.

[cboulanger]

Here's an example : https://github.com/JetBrains/phpstorm-stubs/blob/master/yaml/yaml.php