DOI search engine di Claudio Vergari

Adds a search engine that links to <a href="https://prod.outgoing.prod.webservices.mozgcp.net/v1/0a5e69e4dd2ee7f7c12261784e52818b0007083b085f0931666f1deae713fc65/http%3A//doi.org" rel="nofollow">doi.org</a> (Digital Object Identifier). The source code is available on GitHub: <a href="https://prod.outgoing.prod.webservices.mozgcp.net/v1/7d0579b50d0dc03d69373aa604b4f8915ec1288cf108e0193319d1fc0b7816dd/https%3A//github.com/cvergari/DOI_search" rel="nofollow">https://github.com/cvergari/DOI_search</a>