The main reason of a big version bump is that text api changed and filter images changed.
A lot of things changed and detailed explanations and examples are required to easily jump on the new version.
Please check here: Fabric 2.0 breaking changes - part 1
Below a summary of changs that are the breaking ones:
Changes to selection handling
Removed PathGroup class completely
Introduced requestAnimationFrame for interactive renders, removed some automatic renders.
SVGs are now handled by fabric.Group
transformMatrix property is now deprectated
Filtering system overhaul. Speedups for imageData version and introduced the WEBGL one. More filters added
IText styles are handled by text now. So text is stylable, support multybe, has better caching system and kerning support
Named setters/getters are optional and disabled by default
fabric.Images lost 3 properties: alignX,alignY,meetOrSlice and gained cropX and cropY.
(...more as i remember i ll add them) Dependency updates for node: jsdom bumped to 9.x and node 4 required.
Removed all the JSON and ES5 shimmers. If you need to support non ES5 browsers, do it with external polyfills
Api normalization for fromObject, fromElement, and clone. all are ASYNC.
lockRotation will make ... rotation locked. Will not hide the control
.clipTo is deprecated, please stop using it, i want to do something better.