Adds LICENSE_LIST_VERSION constant to spdx.config

Signed-off-by: Ahmed H. Ismail <ahm3d.hisham@gmail.com>
Adds creation_info field to spdx.document.Document class

Signed-off-by: Ahmed H. Ismail <ahm3d.hisham@gmail.com>
Initial CreationInfo tests

Signed-off-by: Ahmed H. Ismail <ahm3d.hisham@gmail.com>
Initial CreationInfo models

Signed-off-by: Ahmed H. Ismail <ahm3d.hisham@gmail.com>