chore: add gradle task to generate javadoc

Author: qii

library/scene/build.gradle

@@ -16,4 +16,9 @@ dependencies {
     api 'android.arch.lifecycle:runtime:1.1.0'
 }
 
-
+task javadoc(type: Javadoc) {
+    source = android.sourceSets.main.java.srcDirs
+    classpath += project.files(android.getBootClasspath().join(File.pathSeparator))
+    destinationDir = file("../javadoc/scene/")
+    failOnError false
+}

library/scene_ui/build.gradle

@@ -16,3 +16,9 @@ dependencies {
     compile project(path: ':library:scene')
 }
 
+task javadoc(type: Javadoc) {
+    source = android.sourceSets.main.java.srcDirs
+    classpath += project.files(android.getBootClasspath().join(File.pathSeparator))
+    destinationDir = file("../javadoc/scene_ui/")
+    failOnError false
+}