The most relevant change for this release is the implementation of the Gradient class, for iterpolating any given number of CRGB colors in real time, without allocating a palette in memory.
Strip::paint methods now accept Gradient as an alternative to 'CRGB', to fill the string segment with a gradient instead of a solid color. Also, Gradient is directly supported by the HarmonicMotion::setGradient(Gradient *gradient) method, enabling a world of cool new effects. Check out the new effects Sunset and Scan.
Full Changelog: 1.3.0...1.4.0