add hr rule

cms-markdown/src/test/java/com/github/thmarx/cms/markdown/rules/block/HorizontalRuleBlockRuleTest.java

@@ -71,6 +71,31 @@ void test_horizontal_rule_with_before() {
 		Assertions.assertThat(next.render((content) -> content)).isEqualTo("<hr />");
 	}
 
+	@Test
+	void test_horizontal_rule() {
+
+		String input = """
+                 
+                 ---
+                 
+                 """;
+
+		String expected = """
+                    <hr />
+                    """;
+
+		Block next = sut.next(input);
+
+		Assertions.assertThat(next)
+				.isNotNull()
+				.isInstanceOf(HorizontalRuleBlockRule.HRBlock.class);
+
+		Assertions.assertThat(next.render((content) -> content)).isEqualTo("<hr />");
+
+		Assertions.assertThat(next.render(value -> value)).isEqualToIgnoringWhitespace(expected);
+	}
+
+
 	@Test
 	void test_horizontal_rule_issue() {