Feature release

Add ISP, MTT, DQ, IBC, and avx2 optimizations for transforms and DQ.

Changelog

Add experimental support for intra sub partition (ISP) requires disabling some of the AVX2 optimizations, see e32cf4f
Add experimental support for multi type tree (MTT) for intra slices, similarly to ISP requires disabling some AVX2 optimizations e32cf4f
Support for dependent quantization (DQ)
Experimental support for intra block copy (IBC) not guaranteed to have positive impact in most cases, primarly intented for screen content coding
AVX2 optimizations for non-square transform blocks
AVX2 optimizations for DQ
Simplify the dual-tree implementation and enable 2 height chroma block with dual tree
Fix several issues in rate distortion cost calculation

Full Changelog: v0.4.1...v0.8.0