examples: Add smb2mount

examples: Add smb2mount

This is an incomplete playground to add a fuse client based on
the Samba-internal libsmb interfaces.

There's a few fuse smb clients out there, but they all suffer from
Samba not exporting the async internal libsmb interfaces.

We don't export those with an API, because we believe we need the ability
to mess with those interfaces. This is an attempt to create a fully
asynchronous user-space fuse client file system that might make it
easier to mess with fancy SMB features than it would be possible in
a kernel client.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Böhme <slow@samba.org>