function _offsetInToken(ctx) {
        var offset = ctx.pos.ch - ctx.token.start;
        if (offset < 0) {
            console.log("CodeHintUtils: _offsetInToken - Invalid context: the pos what not in the current token!");
        }
        return offset;
    }
@private
in the given context, get the character offset of pos from the start of the token
@param {editor:{CodeMirror}, pos:{ch:{string}, line:{number}}, token:{object}} context
@return {number}