3.1.0:

Major updates

Added support for non-pow2 textures when in WebGL2 mode (deltakosh)
Engine can now be initialized with an existing webgl context (deltakosh)
Introduced behaviors. (Doc here)http://doc.babylonjs.com/overviews/behaviors
Added support for WebGL Occlusion queries. (Doc here)http://doc.babylonjs.com/overviews/occlusionquery
New behaviors for ArcRotateCamera:
- AutoRotation (deltakosh)
- Framing (deltakosh)
- Bouncing (deltakosh)

New camera.storeState() and camera.restoreState() functions to store / restore cameras position / rotation / fov. (Doc here)http://doc.babylonjs.com/tutorials/cameras#state
POW2 textures rescale is now done by shaders (It was previously done using canvas) (deltakosh)
Added SceneLoader.CleanBoneMatrixWeights to force the loader to normalize matrix weights when loading bones (off by default) (deltakosh)
Added camera.onViewMatrixChangedObservable and camera.onProjectionMatrixChangedObservable (deltakosh)
Added support for folders when drag'n'dropping into the sandbox (deltakosh)
Better serialization support (deltakosh)
Introduced performanceMonitor class to get better FPS analysis (deltakosh)
GUI: Added support for pointer move events on projected UI (deltakosh)
Normals are generated automatically by StandardMaterial if meshes do not have normals (deltakosh)
Added mesh.onMaterialChangedObservable to notify when a new material is set (deltakosh)
Improved the SPS perfs for dead or invisible solid particles (jerome)