Add Javadoc to Asciidoc converter

We add a converter between Javadoc and Asciidoc that converts:

 * from a [`DocCommentTree`](https://docs.oracle.com/en/java/javase/17/docs/api/jdk.compiler/com/sun/source/doctree/DocCommentTree.html),
   provided by the `javac` compiler or `javadoc` tool,
 * to an AsciiDoctorJ [`Document`](https://javadoc.io/static/org.asciidoctor/asciidoctorj/3.0.0-alpha.2/org/asciidoctor/ast/Document.html).

We provide a primitive implementation of the AsciiDoctorJ API that
converts the AST back into a text document.

Author: ppkarwasz

log4j-docgen/pom.xml

@@ -27,6 +27,7 @@
   <artifactId>log4j-docgen</artifactId>
 
   <properties>
+    <maven.compiler.release>17</maven.compiler.release>
     <bnd.baseline.fail.on.missing>false</bnd.baseline.fail.on.missing>
   </properties>
 
@@ -38,11 +39,38 @@
       <scope>provided</scope>
     </dependency>
 
+    <dependency>
+      <groupId>org.asciidoctor</groupId>
+      <artifactId>asciidoctorj-api</artifactId>
+      <version>3.0.0-alpha.2</version>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-lang3</artifactId>
+    </dependency>
+
     <dependency>
       <groupId>org.freemarker</groupId>
       <artifactId>freemarker</artifactId>
     </dependency>
 
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-api</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-plugins</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter-api</artifactId>