Remove the JavaScriptFilter function and all the commented out Canvas APIs from the plugin registration function - when these APIs are added, they'll be added solely to the JavaScript side, there's no reason to expose them to AviSynth itself.
Updated the way functions are wrapped, allowing custom AviSynth signatures to (maybe) be used. Also some minor refactoring was started but not actually committed, and the ability to access a frame from JavaScript has been added but not tested.