Let each() take Map in addition to Collection (#110)

* add support for maps for 'each' method.

* add missing imports.

src/main/java/j2html/TagCreator.java

@@ -10,6 +10,8 @@ import j2html.tags.Text;
 import j2html.tags.UnescapedText;
 import java.util.Collection;
 import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Function;
@@ -93,6 +95,10 @@ public class TagCreator {
         return rawHtml(collection.stream().map(mapper.andThen(DomContent::render)).collect(Collectors.joining()));
     }
 
+    public static <I, T> DomContent each(final Map<I, T> map, final Function<Entry<I, T>, DomContent> mapper) {
+        return rawHtml(map.entrySet().stream().map(mapper.andThen(DomContent::render)).collect(Collectors.joining()));
+    }
+
     /**
      * Filters a collection to a list, to be used with {@link j2html.TagCreator#each}
      * Intended usage: {@literal each(filter(numbers, n -> n % 2 == 0), n -> li(n.toString()))}

src/test/java/j2html/tags/TagCreatorTest.java

@@ -2,9 +2,12 @@ package j2html.tags;
 
 import j2html.Config;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Collectors;
+import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
 import static j2html.TagCreator.*;
@@ -18,6 +21,14 @@ public class TagCreatorTest {
 
     List<Employee> employees = Arrays.asList(new Employee(1, "Name 1", "Title 1"), new Employee(2, "Name 2", "Title 2"), new Employee(3, "Name 3", "Title 3"));
 
+    Map<Integer, Employee> employeeMap = new HashMap<>();
+
+    @Before
+    public void setUp() {
+        employeeMap.put(1, new Employee(1, "Name 1", "Title 1"));
+        employeeMap.put(2, new Employee(2, "Name 2", "Title 2"));
+        employeeMap.put(3, new Employee(3, "Name 3", "Title 3"));
+    }
 
     @Test
     public void testDocument() throws Exception {
@@ -92,6 +103,16 @@ public class TagCreatorTest {
         assertThat(j2htmlMap.equals(javaMap), is(true));
     }
 
+    @Test
+    public void testEachWithMap() {
+         final String j2htmlMap = ul().with(
+                 li("Begin list"),
+                each(employeeMap, entry -> li(entry.getKey() + "-" + entry.getValue().name))
+        ).render();
+
+        assertThat(j2htmlMap, is("<ul><li>Begin list</li><li>1-Name 1</li><li>2-Name 2</li><li>3-Name 3</li></ul>"));
+    }
+
     @Test
     public void testFilter() throws Exception {
         String j2htmlFilter = ul().with(