partial application of builtins

currently partial application only works on user-defined functions.

example:

```lisp
(defun sum(x y)
    (+ x y)
)

(sum 1 ..)
;; (.\ (y) (+ 1 y))
```

However, partial application is not yet supported on builtins


```lisp
(+ 1 ..)
;; Error
```
