Add api to get the build version of jail

More for future api usage for other plugins, to determine if the running
version has certain features.

src/main/java/com/graywolf336/jail/JailsAPI.java

@@ -20,6 +20,22 @@ public class JailsAPI {
     protected JailsAPI(JailMain plugin) {
         pl = plugin;
     }
+    
+    /**
+     * Returns the build number, it will return <strong>-1</strong> if an errors occurs.
+     * 
+     * @return the build number of jail or -1 if an error occurred.
+     */
+    public static int getBuildNumber() {
+        String v = pl.getDescription().getVersion();
+        String[] split = v.split("-");
+        
+        try {
+            return Integer.parseInt(split[split.length - 1].replace("b", ""));
+        }catch(NumberFormatException e) {
+            return -1;
+        }
+    }
 
     /**
      * The instance of the {@link JailManager} which contains all the jails and in return prisoners.

src/test/java/test/java/com/graywolf336/jail/TestJailAPI.java

@@ -5,6 +5,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 
@@ -45,6 +46,11 @@ public class TestJailAPI {
         creator.tearDown();
         main = null;
     }
+    
+    @Test
+    public void testBuildNumber() {
+        assertSame("The build version from the api was not 0.", 0, JailsAPI.getBuildNumber());
+    }
 
     @Test
     public void testManagersAreThere() {

src/test/java/test/java/com/graywolf336/jail/util/TestInstanceCreator.java

@@ -92,7 +92,7 @@ public class TestInstanceCreator {
             suppress(constructor(JailMain.class));
             main = PowerMockito.spy(new JailMain());
 
-            PluginDescriptionFile pdf = PowerMockito.spy(new PluginDescriptionFile("Jail", "3.0.0-Test", "com.graywolf336.jail.JailMain"));
+            PluginDescriptionFile pdf = PowerMockito.spy(new PluginDescriptionFile("Jail", "3.0.0-SNAPSHOT-b0", "com.graywolf336.jail.JailMain"));
             when(pdf.getPrefix()).thenReturn("Jail");
             List<String> authors = new ArrayList<String>();
             authors.add("matejdro");