The Classic API changes from 8.1.5* to 1.13.2 (30406) are available here. It also has widgets, events, CVars and enums.
I should probably mention Gethe's FrameXML mirror for completeness
* (The diff is from 8.1.5 instead of 8.1.0 since I only started dumping the api resources in 8.1.5 with the addon sorry)