Updated implementation to support executing outside Django context or w/o `Globals` middleware.

Signed-off-by: Alexander Shvetsov <ashvetsov@definitif.ru>
Added lazy `get_current_user()` method to easier handle cases when user did change within request.

Signed-off-by: Alexander Shvetsov <ashvetsov@definitif.ru>
New version 0.2.1. See ChangeLog for details.

Signed-off-by: Alexander Shvetsov <ashvetsov@definitif.ru>