function getInitialContext(cm, pos) {
        return {
            "editor": cm,
            "pos": pos,
            "token": cm.getTokenAt(pos, true)
        };
    }
Creates a context object for the given editor and position, suitable for passing to the
move functions.
@param {!CodeMirror} cm
@param {!{ch:number, line:number}} pos
@return {!{editor:!CodeMirror, pos:!{ch:number, line:number}, token:Object}}