Two new wrappers:
Notmuch::Database.find_message(id) => Notmuch::Message or nil
Notmuch::Database.find_message_by_filename(path) => Notmuch::Message or nil
Let the user destroy objects that she wants explicitly.
It's not possible to specify the order objects are garbage collected.
See id:86y6f8v838.fsf@harikalardiyari.ev on ruby-talk for more
information.