- Replace MixBlend/MixDirection with bool fromSetup/add/out in all timeline apply() signatures
- Remove MixBlend.h and MixDirection.h (no longer used)
- Add Timeline::_additive and _instant fields
- Replace TrackEntry holdPrevious/interruptAlpha/mixBlend with additive/keepHold
- Rewrite AnimationState hold system with bitmask (Subsequent/First/Hold/HoldFirst)
- Rewrite applyMixingFrom alpha computation
- Rename Skin::AttachmentMap::Entry::_name to _placeholderName
- Fix SkeletonBinary::readLong() sign extension bug truncating 64-bit hashes
- Fix SkeletonSerializer sequence and bones null/empty parity with Java
- Add transition frame testing to HeadlessTest
- Port all doc updates from spine-libgdx
- spine-cpp/spine-cpp was moved into spine-cpp directory, so spine-cpp/spine-cpp/src -> spine-cpp/src, spine-cpp/spine-cpp/include -> spine-cpp/include
- Added scaffold for DebugPrinter to be used by runtime comparison tests
- Added build.sh
