Add module-info.java as multi release

pom.xml

@@ -1,6 +1,6 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0"
-	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+		 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>micycle</groupId>
 	<artifactId>clipper2</artifactId>
@@ -27,6 +27,34 @@
 						</path>
 					</annotationProcessorPaths>
 				</configuration>
+				<executions>
+					<execution>
+						<id>compile-java-9</id>
+						<phase>compile</phase>
+						<goals>
+							<goal>compile</goal>
+						</goals>
+						<configuration>
+							<release>9</release>
+							<compileSourceRoots>
+								<compileSourceRoot>${project.basedir}/src/main/java9</compileSourceRoot>
+							</compileSourceRoots>
+							<multiReleaseOutput>true</multiReleaseOutput>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-jar-plugin</artifactId>
+				<version>3.3.0</version>
+				<configuration>
+					<archive>
+						<manifestEntries>
+							<Multi-Release>true</Multi-Release>
+						</manifestEntries>
+					</archive>
+				</configuration>
 			</plugin>
 			<plugin>
 				<groupId>pw.krejci</groupId>
@@ -46,7 +74,7 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-surefire-plugin</artifactId>
-				<version>2.22.2</version>
+				<version>3.1.2</version>
 				<configuration>
 					<forkCount>4</forkCount>
 					<reuseForks>false</reuseForks>
@@ -55,7 +83,7 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-source-plugin</artifactId>
-				<version>3.2.1</version>
+				<version>3.3.0</version>
 				<executions>
 					<execution>
 						<id>attach-sources</id>
@@ -68,10 +96,11 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-javadoc-plugin</artifactId>
-				<version>3.5.0</version>
+				<version>3.6.0</version>
 				<configuration>
 					<failOnError>false</failOnError>
 					<doclint>all</doclint>
+					<source>8</source>
 				</configuration>
 				<executions>
 					<execution>

src/main/java9/module-info.java

@@ -0,0 +1,9 @@
+module clipper2 {
+    exports clipper2;
+    exports clipper2.core;
+    exports clipper2.engine;
+    exports clipper2.offset;
+    exports clipper2.rectclip;
+
+    exports tangible;
+}