Update javadoc and switch to Java release 17

Enhance MjmlDocument Javadoc to better describe the record and add an @param for the root node. In pom.xml, replace the maven.compiler.source/target properties with maven.compiler.release and update the maven-compiler-plugin configuration to use <release>17. This simplifies Java version configuration and ensures the project is built with the Java 17 release flag.

Author: jcputney

mjml-java-core/src/main/java/dev/jcputney/mjml/parser/MjmlDocument.java

@@ -1,8 +1,12 @@
 package dev.jcputney.mjml.parser;
 
 /**
- * Parsed MJML document model containing the root node and convenience accessors for head and body
- * sections.
+ * Represents an MJML document's structure, containing a root node
+ * and methods to access key elements such as the head and body nodes.
+ * This class encapsulates the MJML document's logical model, allowing
+ * for the retrieval of specific parts of its structure.
+ *
+ * @param root the root {@code <mjml>} node of the document
  */
 public record MjmlDocument(MjmlNode root) {
 

pom.xml

@@ -47,8 +47,7 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
-        <maven.compiler.source>17</maven.compiler.source>
-        <maven.compiler.target>17</maven.compiler.target>
+        <maven.compiler.release>17</maven.compiler.release>
         <junit.version>6.0.2</junit.version>
         <version.plugin.central-publishing>0.10.0</version.plugin.central-publishing>
         <version.plugin.gpg>3.2.8</version.plugin.gpg>
@@ -79,8 +78,7 @@
                     <artifactId>maven-compiler-plugin</artifactId>
                     <version>3.15.0</version>
                     <configuration>
-                        <source>17</source>
-                        <target>17</target>
+                        <release>17</release>
                     </configuration>
                 </plugin>
                 <plugin>