Rework smackx.address (XEP-0033: Extended Stanza Addressing)

- Make MultipleAddress.Type a enum
- Change the signature of the methods to use Collection instead of List
- Use for-each loops instead of iterators
- Switch Provider to new provider pattern (using switch-case)
- Use XmlStringBuilder (extend the API by two new methods)

smack-core/src/main/java/org/jivesoftware/smack/util/XmlStringBuilder.java

@@ -98,6 +98,10 @@ public class XmlStringBuilder implements Appendable, CharSequence {
         return this;
     }
 
+    public XmlStringBuilder halfOpenElement(NamedElement namedElement) {
+        return halfOpenElement(namedElement.getElementName());
+    }
+
     public XmlStringBuilder openElement(String name) {
         halfOpenElement(name).rightAngleBracket();
         return this;
@@ -207,6 +211,13 @@ public class XmlStringBuilder implements Appendable, CharSequence {
         return this;
     }
 
+    public XmlStringBuilder optBooleanAttribute(String name, boolean bool) {
+        if (bool) {
+            sb.append(' ').append(name).append("='true'");
+        }
+        return this;
+    }
+
     public XmlStringBuilder xmlnsAttribute(String value) {
         optAttribute("xmlns", value);
         return this;