V2.60 docs as compressed CHM here, including SDK stuff + Aivsynth v3 (v2.58) and v6 (v2.60) Avisynth Headers.h
AvisynthEngHelp SDK26_FINAL-2015-05-31 (~4.6MB):-
http://www.mediafire.com/file/62mphc...2015-05-31.zip
Sling it on a hotkey eg CTRL/ALT/H.