x265: updated to 3.2

Version 3.2

New features
1. 3-level hierarchical motion estimation using :option:`--hme` and :option:`--hme-search`.
2. New AQ mode (:option:`--aq-mode` 4) with variance and edge information.
3. :option:`selective-sao` to selectively enable SAO at slice level.

Enhancements to existing features
1. New implementation of :option:`--refine-mv` with 3 refinement levels.

Encoder enhancements
1. Improved quality in the frames following dark scenes in ABR mode.

API changes
1. Additions to x265_param structure to support the newly added features :option:`--hme`, :option:`--hme-search` and :option:`selective-sao`.

Bug fixes
1. Fixed encoder crash with :option:`--zonefile` during failures in encoder_open().
2. Fixed JSON11 build errors with HDR10+ on MacOS high sierra.
3. Signalling out of range scaling list data fixed.
4. Inconsistent output fix for 2-pass rate-control with cutree ON.

Known issues
1. Build dependency on changeset cf37911 of SVT-HEVC.

(adam)