add changelog for upcoming release 0.8.5

Signed-off-by: Armin Tänzer <armin.taenzer@tngtech.com>

Remove mentions that SPDX 3 is not released yet

Signed-off-by: Arthit Suriyawongkul <arthit@gmail.com>

spdx-tools v0.8.3

spdx-tools v0.8.2

spdx-tools v0.8.1

spdx-tools v0.8.0

spdx-tools v0.8.0rc3

python spdx tools v0.8.0rc2

python spdx tools v0.8.0rc1

python spdx tools v0.8.0a3