NavDB version 0.4 (beta) released

https://navdb.io/2019/01/18/navdb-version-0-4-beta-released/

Changes:

1. New syntax for temporary keys with the expires keyword.

2. Performance enhancements in the NavDB server.

3. SCRAM authentication (admin user only for now).

4. New PHP 7 client.

5. Separation of reusable code into libnav (Apache 2.0 license).

6. Upgrade to Boost v1.69.0 (from v1.68.0).