This library provides extra record operations.
Returns #t if obj is record type, otherwise #f.
Name must be symbol. Rtd must be record type descriptor. Rcd must be record constructor descriptor.
Associates given rcd to gien rtd.
NOTE: this procedure doesn't create fresh record type but modifies given arguments destructively.
Record-type must be record type.
Returns associated rtd from record-type.
Record-type must be record type.
Returns associated rcd from record-type.
Note: These procedures are not for using casually.