Make EmbeddedPostgres implements AutoCloseable (#131)

This allows to use it in a try-with-resources statement, in order to
have it automatically closed/stopped.

README.md

@@ -63,6 +63,10 @@ conn.close();
 postgres.stop();
 ```
 
+Note that EmbeddedPostgres implements [java.lang.AutoCloseable](https://docs.oracle.com/javase/7/docs/api/java/lang/AutoCloseable.html), 
+which means that you can use it with a [try-with-resources](https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html) 
+statement (in Java >= 7) to have it automatically stopped.
+
 ### How to avoid archive extraction on every run
 
 You can specify the cached artifact store to avoid archives downloading and extraction (in case if a directory remains on every run).

src/main/java/ru/yandex/qatools/embed/postgresql/EmbeddedPostgres.java

@@ -26,7 +26,7 @@
 /**
  * Helper class simplifying the start up configuration for embedded postgres
  */
-public class EmbeddedPostgres {
+public class EmbeddedPostgres implements AutoCloseable {
     public static final String DEFAULT_USER = "postgres";//NOSONAR
     public static final String DEFAULT_PASSWORD = "postgres";//NOSONAR
     public static final String DEFAULT_DB_NAME = "postgres";//NOSONAR
@@ -215,4 +215,9 @@ private String formatConnUrl(PostgresConfig config) {
     public void stop() {
         getProcess().orElseThrow(() -> new IllegalStateException("Cannot stop not started instance!")).stop();
     }
+
+    @Override
+    public void close() {
+        this.stop();
+    }
 }