CHANGES_NEXT_RELEASE

- Add: CORS Preflight Requests support for all NGSIv2 resources, -corsMaxAge switch, CORS exposed headers (#501, #3030)
- Fix: null not working in q/mq filter in subscriptions (#2998)
- Fix: case-sensitive header duplication (e.g. "Content-Type" and "Content-type") in custom notifications (#2893)
- Fix: bug in GTE and LTE operations in query filters (q/mq), both for GET operations and subscriptions (#2995)
- Fix: Wrong "max one service-path allowed for subscriptions" in NGSIv2 subscription operation (#2948)