Add support to lease and notify

[lskvcxz]

Hi,
libsmb2 currently does not support negotiating leases with samba servers, nor does it support initiating notify listening events and receiving or parsing notify messages. We hope to add support in this area

[sahlberg]

Sounds good.
I would suggest you start with adding the low level SMB2 function calls to do this.
Then to surface this to applications.... There is no posix interface for this but I feel like having a layer that mimics the linux inotify interface would work well here. Try to do that.

libsmb2 is not thread-safe at the moment so you may want to limit its use to only be available for the async interface.