add step attribute (#150)

Author: arnzel

src/main/java/j2html/tags/Tag.java

@@ -253,6 +253,10 @@ public T withStyle(String style) {
         return attr(Attr.STYLE, style);
     }
 
+    public T withStep(String step) {
+        return attr(Attr.STEP, step);
+    }
+
     public T withValue(String value) {
         return attr(Attr.VALUE, value);
     }

src/test/java/j2html/tags/ConvenienceMethodTest.java

@@ -36,6 +36,7 @@ public void testAllConvenienceMethods() throws Exception {
         assertThat(link().withRel("stylesheet").render(), is("<link rel=\"stylesheet\">"));
         assertThat(link().withRole("role").render(), is("<link role=\"role\">"));
         assertThat(img().withSrc("/img/test.png").render(), is("<img src=\"/img/test.png\">"));
+        assertThat(input().withStep("0.1").render(), is("<input step=\"0.1\">"));
         assertThat(div().withStyle("background:red;").render(), is("<div style=\"background:red;\"></div>"));
         assertThat(input().withValue("test-value").render(), is("<input value=\"test-value\">"));
     }