Introduce direct .min/.max on Bags/BagHashes

Actually inspired by a code example of TheDamian that looked hacky, since one
of the more common uses of Bags/BagHashes are to find out the frequence of
things, and hence you probably want to know the lowest/highest frequency quite
often as well.

src/core/Bag.pm

@@ -1,10 +1,13 @@
 my class Bag does Baggy {
     has Int $!total;
+    has Int $!min;
+    has Int $!max;
     has $!WHICH;
 
-    method total {
-        $!total //= [+] %!elems.values.map( { .value } );
-    }
+    method total (--> Int) { $!total //= [+] self.values }
+    method min   (--> Int) { $!min //= self.values.min }
+    method max   (--> Int) { $!max //= self.values.max }
+
     submethod WHICH { $!WHICH }
     submethod BUILD (:%elems)  {
         my @keys := %elems.keys.sort;

src/core/Baggy.pm

@@ -8,6 +8,8 @@ my role Baggy does QuantHash {
     method kv { %!elems.values.map( {.key, .value} ) }
     method elems(--> Int) { %!elems.elems }
     method total(--> Int) { [+] self.values }
+    method min(--> Int) { self.values.min }
+    method max(--> Int) { self.values.max }
     method exists ($k --> Bool) {  # is DEPRECATED doesn't work in settings
         DEPRECATED("the :exists adverb");
         self.exists_key($k);