Maven POM: add a few javadoc links.

Author: carlosame

pom.xml

@@ -51,6 +51,11 @@
 			<artifactId>maven-javadoc-plugin</artifactId>
 			<configuration>
 				<source>7</source>
+				<links>
+					<link>https://docs.oracle.com/javase/7/docs/api/</link>
+					<link>https://css4j.github.io/api/1.0/</link>
+					<link>https://about.validator.nu/htmlparser/apidocs/</link>
+				</links>
 			</configuration>
 		</plugin>
 		<plugin>