Add new typesafe config integration extras module

Motivation:
Current implemenation does not have any integration with popular config library.

Modifications:
Added extras module with Typesafe Config integration and provided AHC config wrapper for mentioned lib.

Result:
AsyncHttpClient can be initialized with Typesafe Config file.

Author: coutoPL

client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClientConfig.java

@@ -24,6 +24,7 @@
 import org.asynchttpclient.channel.ChannelPool;
 import org.asynchttpclient.channel.DefaultKeepAliveStrategy;
 import org.asynchttpclient.channel.KeepAliveStrategy;
+import org.asynchttpclient.config.AsyncHttpClientConfigDefaults;
 import org.asynchttpclient.cookie.CookieStore;
 import org.asynchttpclient.cookie.ThreadSafeCookieStore;
 import org.asynchttpclient.filter.IOExceptionFilter;
@@ -49,18 +50,6 @@
  */
 public class DefaultAsyncHttpClientConfig implements AsyncHttpClientConfig {
 
-  private static final String AHC_VERSION;
-
-  static {
-    try (InputStream is = DefaultAsyncHttpClientConfig.class.getResourceAsStream("/ahc-version.properties")) {
-      Properties prop = new Properties();
-      prop.load(is);
-      AHC_VERSION = prop.getProperty("ahc.version", "UNKNOWN");
-    } catch (IOException e) {
-      throw new ExceptionInInitializerError(e);
-    }
-  }
-
   // http
   private final boolean followRedirect;
   private final int maxRedirects;
@@ -302,7 +291,7 @@ private DefaultAsyncHttpClientConfig(// http
 
   @Override
   public String getAhcVersion() {
-    return AHC_VERSION;
+    return AsyncHttpClientConfigDefaults.AHC_VERSION;
   }
 
   // http

client/src/main/java/org/asynchttpclient/config/AsyncHttpClientConfigDefaults.java

@@ -20,6 +20,7 @@
     <module>rxjava2</module>
     <module>simple</module>
     <module>retrofit2</module>
+    <module>typesafeconfig</module>
   </modules>
 
   <dependencies>

extras/pom.xml

@@ -0,0 +1,34 @@
+# Async-http-client and Typesafe Config integration
+
+An `AsyncHttpClientConfig` implementation integrating [Typesafe Config][1] with Async Http Client.
+## Download
+
+Download [the latest JAR][2] or grab via [Maven][3]:
+
+```xml
+<dependency>
+  <groupId>org.asynchttpclient</groupId>
+  <artifactId>async-http-client-extras-typesafeconfig</artifactId>
+  <version>latest.version</version>
+</dependency>
+```
+
+or [Gradle][3]:
+
+```groovy
+compile "org.asynchttpclient:async-http-client-extras-typesafeconfig:latest.version"
+```
+
+ [1]: https://github.com/lightbend/config
+ [2]: https://search.maven.org/remote_content?g=org.asynchttpclient&a=async-http-client-extras-typesafeconfig&v=LATEST
+ [3]: http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22org.asynchttpclient%22%20a%3A%22async-http-client-extras-typesafeconfig%22
+ [snap]: https://oss.sonatype.org/content/repositories/snapshots/
+
+## Example usage
+
+```java
+// creating async-http-client with Typesafe config
+com.typesafe.config.Config config = ...
+AsyncHttpClientTypesafeConfig ahcConfig = new AsyncHttpClientTypesafeConfig(config);
+AsyncHttpClient client = new DefaultAsyncHttpClient(ahcConfig);
+```

extras/typesafeconfig/README.md

@@ -0,0 +1,26 @@
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <artifactId>async-http-client-extras-parent</artifactId>
+    <groupId>org.asynchttpclient</groupId>
+    <version>2.2.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>async-http-client-extras-typesafe-config</artifactId>
+  <name>Asynchronous Http Client Typesafe Config Extras</name>
+  <description>The Async Http Client Typesafe Config Extras.</description>
+
+  <properties>
+    <typesafeconfig.version>1.3.2</typesafeconfig.version>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>com.typesafe</groupId>
+      <artifactId>config</artifactId>
+      <version>${typesafeconfig.version}</version>
+    </dependency>
+  </dependencies>
+</project>