added empty<Comp> to the registry

src/registry.hpp

@@ -256,6 +256,11 @@ public:
         return available.size() == count;
     }
 
+    template<typename Comp>
+    bool empty() const noexcept {
+        return pool.template empty<Comp>();
+    }
+
     entity_type create() noexcept {
         entity_type entity;
 

test/registry.cpp

@@ -10,9 +10,15 @@ TEST(DefaultRegistry, Functionalities) {
     ASSERT_EQ(registry.capacity(), registry_type::size_type{0});
     ASSERT_TRUE(registry.empty());
 
+    ASSERT_TRUE(registry.empty<int>());
+    ASSERT_TRUE(registry.empty<char>());
+
     registry_type::entity_type e1 = registry.create();
     registry_type::entity_type e2 = registry.create<int, char>();
 
+    ASSERT_FALSE(registry.empty<int>());
+    ASSERT_FALSE(registry.empty<char>());
+
     ASSERT_NE(e1, e2);
 
     ASSERT_FALSE(registry.has<int>(e1));