Introduce Smack's Modular Connection Architecture

This is a complete redesign of what was previously
XmppNioTcpConnection. The new architecture allows to extend an XMPP
client to server (c2s) connection with new transport bindings and
other extensions.

smack-java8-full/src/main/java/org/jivesoftware/smack/full/ModularXmppClientToServerConnectionTool.java

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+/**
+ *
+ * Copyright 2018-2020 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack.full;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.PrintWriter;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.jivesoftware.smack.c2s.ModularXmppClientToServerConnectionConfiguration;
+
+import org.jxmpp.stringprep.XmppStringprepException;
+
+public class ModularXmppClientToServerConnectionTool {
+
+    @SuppressWarnings("DefaultCharset")
+    public static void main(String[] args) throws XmppStringprepException, FileNotFoundException {
+
+        final PrintWriter pw;
+        final boolean breakStateName;
+
+        switch (args.length) {
+        case 0:
+            pw = new PrintWriter(System.out);
+            breakStateName = false;
+            break;
+        case 1:
+            Path outputFilePath = Paths.get(args[0]);
+            File outputFile = outputFilePath.toFile();
+            if (outputFile.exists()) {
+                outputFile.delete();
+            }
+            pw = new PrintWriter(outputFile);
+            breakStateName = true;
+            break;
+        default:
+            throw new IllegalArgumentException("At most one argument allowed");
+        }
+
+        printStateGraph(pw, breakStateName);
+        pw.flush();
+    }
+
+    public static void printStateGraph(PrintWriter pw, boolean breakStateName) throws XmppStringprepException {
+        ModularXmppClientToServerConnectionConfiguration.Builder configurationBuilder = ModularXmppClientToServerConnectionConfiguration.builder()
+                        .setUsernameAndPassword("user", "password")
+                        .setXmppDomain("example.org");
+
+        ModularXmppClientToServerConnectionConfiguration configuration = configurationBuilder.build();
+
+        configuration.printStateGraphInDotFormat(pw, breakStateName);
+
+        pw.flush();
+    }
+
+}

smack-java8-full/src/main/java/org/jivesoftware/smack/full/package-info.java

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+/**
+ *
+ * Copyright 2020 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * The Smack XMPP client library.
+
+ * <h2>Modular XMPP c2s connection</h2>
+ * <p>
+ * The graph below shows the current states of the modular xmpp client connection. Only some states are final states,
+ * most states are intermediate states in order to reach a final state.
+ * </p>
+ * <img src="doc-files/ModularXmppClientToServerConnectionStateGraph.png" alt="The state graph of XmppNioTcpConnection">
+ */
+package org.jivesoftware.smack.full;