Added series project

exercises/series/build.gradle

+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  testCompile "junit:junit:4.12"
+  testCompile "org.assertj:assertj-core:3.2.0"
+}
+test {
+  testLogging {
+    exceptionFormat = 'full'
+    events = ["passed", "failed", "skipped"]
+  }
+}

exercises/settings.gradle

 include 'roman-numerals'
 include 'prime-factors'
 include 'scrabble-score'
+include 'series'
 include 'sieve'
 include 'simple-cipher'
 include 'simple-linked-list'