Add plugin version in es-plugin.properties

With elastic/elasticsearch#2784, we can now add plugin version in `es-plugin.properties` file.

It will only be used with elasticsearch 1.0.0 and upper. No need to push it in 1.x branch.

Closes #21.

Author: dadoonet

pom.xml

@@ -94,6 +94,16 @@
     </dependencies>
 
     <build>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+                <includes>
+                    <include>**/*.properties</include>
+                </includes>
+            </resource>
+        </resources>
+
         <testResources>
             <testResource>
                 <directory>src/test/resources</directory>

src/main/resources/es-plugin.properties

@@ -1,2 +1,3 @@
 plugin=org.elasticsearch.plugin.river.wikipedia.WikipediaRiverPlugin
+version=${project.version}