Cleanup Maven Publishing

* Ensure that Maven Source Jars are published
* Ensure that Javadoc is published
* Ensure Maven pom includes required information for central

Fixes gh-36

spring-session/build.gradle

@@ -1,5 +1,5 @@
 apply from: JAVA_GRADLE
-apply plugin: 'propdeps-maven'
+apply from: MAVEN_GRADLE
 
 project.conf2ScopeMappings.addMapping(MavenPlugin.TEST_COMPILE_PRIORITY + 1, project.configurations.getByName("integrationTestCompile"), Conf2ScopeMappingContainer.TEST)
 project.conf2ScopeMappings.addMapping(MavenPlugin.TEST_COMPILE_PRIORITY + 2, project.configurations.getByName("integrationTestRuntime"), Conf2ScopeMappingContainer.TEST)
@@ -23,6 +23,38 @@ dependencies {
 
     jacoco "org.jacoco:org.jacoco.agent:0.6.2.201302030002:runtime"
 }
+
+javadoc {
+    description = "Generates project-level javadoc for use in -javadoc jar"
+
+    options.memberLevel = org.gradle.external.javadoc.JavadocMemberLevel.PROTECTED
+    options.author = true
+    options.header = project.name
+    options.links(project.ext.javadocLinks)
+    options.addStringOption('Xdoclint:none', '-quiet')
+
+    // suppress warnings due to cross-module @see and @link references;
+    // note that global 'api' task does display all warnings.
+    logging.captureStandardError LogLevel.INFO
+    logging.captureStandardOutput LogLevel.INFO // suppress "## warnings" message
+}
+
+task sourcesJar(type: Jar, dependsOn: classes) {
+    classifier = 'sources'
+    from sourceSets.main.allSource
+    // don't include or exclude anything explicitly by default. See SPR-12085.
+}
+
+task javadocJar(type: Jar) {
+    classifier = "javadoc"
+    from javadoc
+}
+
+artifacts {
+    archives sourcesJar
+    archives javadocJar
+}
+
 test {
     jvmArgs "-javaagent:${configurations.jacoco.asPath}=destfile=${buildDir}/jacoco.exec,includes=${project.group}.*"
 }