Add Volan - Another simplified validation library.

README.md

 * [DMS Filter](https://github.com/rdohms/DMS-Filter) - An annotation filtering library.
 * [MetaYaml](https://github.com/romaricdrigon/MetaYaml) - A schema validation library that supports YAML, JSON and XML.
 * [ISO-codes](https://github.com/ronanguilloux/IsoCodes) - A library for validating various ISO and ZIP codes (IBAN, SWIFT/BIC, BBAN, VAT, SSN, UKNIN).
+* [Volan](https://github.com/serkin/Volan) - Another simplified validation library.
 
 ## API
 *Libraries and web tools for developing APIs.*