Gradle example improvements (#22)

* Add a filter on the repository

* Use new notation for sources and javadoc jars

Author: jmini

usage-examples/jdt-gradle-example/build.gradle

@@ -8,6 +8,8 @@ wrapper {
 }
 
 java {
+    withJavadocJar()
+    withSourcesJar()
     toolchain {
         languageVersion = JavaLanguageVersion.of(8)
     }
@@ -17,21 +19,14 @@ java {
 repositories {
     maven {
         url 'https://raw.githubusercontent.com/jmini/ecentral/HEAD/repo'
+        content {
+            includeGroup 'fr.jmini.ecentral'
+        }
     }
     mavenCentral()
 }
 //end::repositories[]
 
-task sourcesJar(type: Jar, dependsOn: classes) {
-    classifier = 'sources'
-    from sourceSets.main.allSource
-}
-
-task javadocJar(type: Jar) {
-    from javadoc
-    classifier = 'javadoc'
-}
-
 //tag::dependencies[]
 dependencies {
     implementation platform('fr.jmini.ecentral:eclipse-platform-dependencies:4.14')
@@ -59,4 +54,4 @@ spotless {
     // available versions are: https://github.com/diffplug/spotless/tree/master/lib-extra/src/main/resources/com/diffplug/spotless/extra/eclipse_jdt_formatter
     eclipse('4.13.0').configFile('.settings/org.eclipse.jdt.core.prefs')
   }
-}
+}