Add `bag-empty?`

syndicate/bag.rkt

@@ -8,6 +8,7 @@
          bag-ref
          bag-clear!
          bag-member?
+         bag-empty?
          bag-key-count
          in-bag
          in-bag/count
@@ -52,6 +53,7 @@
 
 (define bag-clear! hash-clear!)
 (define bag-member? hash-has-key?)
+(define bag-empty? hash-empty?)
 (define bag-key-count hash-count)
 
 (define-syntax-rule (in-bag piece ...) (in-hash-keys piece ...))