Native record

native record primitives are defined in (picrin record-primitive)
- (make-record rectype)
- (record-of? record rectype)
- (record-ref record rectype field-name)
- (record-set! record rectype field-name value)

define-record-type is implemented using these primitives.
Curretly, record-type is also record-object. Its record-type is #t, and have only name field.
rectype is used for type check. Type check is necessary to distinguish different record-type with same slot name.