Upgrade Maven project to Spock 2.0-M3, ... (#35)

* Sync Spock dependency versions
* Now that Spock no longer depends on 'groovy-all', for the database test it was
  necessary to add 'groovy-sql'.
* Make feature method names friendlier in unrolled DatabaseDrivenSpec
* Make IncludeExcludeExtensionSpec print messages
  This way the user can verify visually that in-/excludes actually work as
  expected.
* Upgrade Groovy 2.5.12 -> 2.5.13
* Slightly adjust README.adoc 
  Change passive style "all feedback is appreciated" to active style "we
  appreciate all feedback".

pom.xml

@@ -11,6 +11,7 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+    <groovy.version>2.5.13</groovy.version>
   </properties>
 
   <build>
@@ -60,7 +61,7 @@
       <dependency>
         <groupId>org.spockframework</groupId>
         <artifactId>spock-bom</artifactId>
-        <version>2.0-M1-groovy-2.5</version>
+        <version>2.0-M3-groovy-2.5</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>
@@ -83,24 +84,24 @@
     <dependency> <!-- use a specific Groovy version rather than the one specified by spock-core -->
       <groupId>org.codehaus.groovy</groupId>
       <artifactId>groovy</artifactId>
-      <version>2.5.8</version>
+      <version>${groovy.version}</version>
     </dependency>
     <dependency> <!-- enables mocking of classes (in addition to interfaces) -->
       <groupId>net.bytebuddy</groupId>
       <artifactId>byte-buddy</artifactId>
-      <version>1.9.3</version>
+      <version>1.10.10</version>
       <scope>test</scope>
     </dependency>
-    <dependency> <!-- enables mocking of classes without default constructor (together with CGLIB) -->
+    <dependency> <!-- enables mocking of classes without default constructor (together with ByteBuddy or CGLIB) -->
       <groupId>org.objenesis</groupId>
       <artifactId>objenesis</artifactId>
-      <version>2.6</version>
+      <version>3.1</version>
       <scope>test</scope>
     </dependency>
     <dependency> <!-- only required if Hamcrest matchers are used -->
       <groupId>org.hamcrest</groupId>
       <artifactId>hamcrest-core</artifactId>
-      <version>1.3</version>
+      <version>2.2</version>
       <scope>test</scope>
     </dependency>
     <!-- Dependencies used by examples in this project (not required for using Spock) -->
@@ -109,6 +110,11 @@
       <artifactId>h2</artifactId>
       <version>1.4.197</version>
     </dependency>
+    <dependency>
+      <groupId>org.codehaus.groovy</groupId>
+      <artifactId>groovy-sql</artifactId>
+      <version>${groovy.version}</version>
+    </dependency>
   </dependencies>
 
   <repositories>