Log Message:
libfilezilla: update to 0.16.0.

2019-04-21 - libfilezilla 0.16.0 released
New features:

    Add fz::socket
    Add operator*= to fz::duration
    fz::event_loop can now also be created using fz::thread_pool or threadless.

Bugfixes and minor changes:

    fz::async_task now releases the thread back to the pool immediately when the \ 
task has completed without waiting for the join
    *nix: Fix file descriptor leaks on exec()