Implement Table#hash

Copy the implemenation from Hash#hash, which produces the same hash
regardless of order of keys

spec/table_spec.cr

@@ -164,6 +164,12 @@ describe AMQ::Protocol::Table do
     t1["x-delay"]?.should be_nil
     t1.to_h.should eq({"x-stream-offset" => 1i64})
   end
+
+  it "hash values for two semantically tables are the same" do
+    t1 = AMQ::Protocol::Table.new({a: 1, b: "foo"})
+    t2 = AMQ::Protocol::Table.new({b: "foo", a: 1})
+    t1.hash.should eq t2.hash
+  end
 end
 
 # Verifies bugfix for Sub-table memory corruption

src/amq/protocol/table.cr

@@ -167,6 +167,23 @@ module AMQ
         true
       end
 
+      # See `Object#hash(hasher)`
+      def hash(hasher)
+        # Copied from Hash#hash
+        # The hash value must be the same regardless of the
+        # order of the keys.
+        result = hasher.result
+
+        each do |key, value|
+          copy = hasher
+          copy = key.hash(copy)
+          copy = value.hash(copy)
+          result &+= copy.result
+        end
+
+        result.hash(hasher)
+      end
+
       def delete(key : String)
         ensure_writeable
         @io.rewind