v4.0.0

• Version 4.0.0
  • Breaking: Requires C++17
  • Breaking: tweeny::from() returns a builder; call .build() to create a tween
  • Breaking: Tweens are immutable after build() (keyframes, durations, and easings cannot be changed)
  • Breaking: Durations must be uint32_t (during(60U)); step() accepts int32_t frame deltas only (no percentage mode)
  • Breaking: seek() accepts uint32_t absolute frame positions only (no percentage mode)
  • Breaking: Multi-value tweens return std::tuple instead of std::array
  • Breaking: Callbacks use on(event::…) with event::response return values instead of onStep() / onSeek()
  • Breaking: forward() / backward() removed; use negative step() values to move backward
  • Breaking: Headers moved to include/tweeny/; include as #include <tweeny/tweeny.h>
  • Breaking: Removed easing::enumerated and string-based via("linear") easing selection
  • New event types: complete, keyframeEnter, keyframeLeave, update
  • New methods: peek(), peek(frame), progress(), jump(keyframe)
  • Restructured internals under tweeny::detail; easing split into per-function headers
  • Added Catch2 test suite and Doxygen manual with v3-to-v4 migration guide
  • CMake: C++17 enforcement, FILE_SET HEADERS, optional tests and single-header target (via uvx + quom)
  • Fixed exponential easing endpoints (position == 0 / == 1) to match Penner behavior
  • Expanded tests: Penner reference samples for bundled easings (direct + via); def/stepped (including multi-keyframe stepped); seek/step/jump vs peek consistency
  • GitHub Actions CI (Ubuntu, Catch2, build + ctest)
  • scripts/create-release.sh — release from an existing tag (docs sync to gh-pages, single-header asset, GitHub Release)
  • README: CMake install + find_package(Tweeny); fixed installed include interface so #include <tweeny/tweeny.h> works after install
  • Docs: event::update, progress(), honest zero-during() behavior; Doxygen styling aligned with the site
  • Removed sandbox CMake option/target