Updating Changes file for next tag 8.0.0-a13.
Updating Changes file for next tag 8.0.0-a13.

appleseedhq/cortex,danieldresser/cortex,davidsminor/cortex,danieldresser/cortex,davidsminor/cortex,hradec/cortex,davidsminor/cortex,hradec/cortex,danieldresser/cortex,appleseedhq/cortex,lento/cortex,goddardl/cortex,goddardl/cortex,danieldresser/cortex,lento/cortex,goddardl/cortex,lento/cortex,hradec/cortex,davidsminor/cortex,appleseedhq/cortex