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".

src/test/groovy/DataDrivenSpec.groovy

@@ -16,7 +16,6 @@
 
 import spock.lang.*
 
-@Unroll
 class DataDrivenSpec extends Specification {
   def "maximum of two numbers"() {
     expect:
@@ -55,4 +54,4 @@ class DataDrivenSpec extends Specification {
       name == "Fred" ? "Male" : "Female"
     }
   }
-}
+}

src/test/groovy/DatabaseDrivenSpec.groovy

@@ -20,18 +20,18 @@ import spock.lang.Specification
 
 class DatabaseDrivenSpec extends Specification {
   @Shared sql = Sql.newInstance("jdbc:h2:mem:", "org.h2.Driver")
-  
+
   // insert data (usually the database would already contain the data)
   def setupSpec() {
     sql.execute("create table maxdata (id int primary key, a int, b int, c int)")
-    sql.execute("insert into maxdata values (1, 3, 7, 7), (2, 5, 4, 5), (3, 9, 9, 9)")
+    sql.execute("insert into maxdata values (1, 3, 7, 7), (2, 5, 4, 5), (3, 9, 9, 9), (4, 2, -3, 2)")
   }
 
-  def "maximum of two numbers"() {
+  def "Maximum of #a and #b is #c"() {
     expect:
     Math.max(a, b) == c
 
     where:
     [a, b, c] << sql.rows("select a, b, c from maxdata")
   }
-}
+}

src/test/groovy/IncludeExcludeExtensionSpec.groovy

@@ -49,15 +49,18 @@ import spock.lang.Specification
 class IncludeExcludeExtensionSpec extends Specification {
   @Fast
   def "a fast method"() {
+    println "fast"
     expect: true
   }
 
   @Slow
   def "a slow method"() {
+    println "slow"
     expect: true
   }
 
   def "a neither fast nor slow method"() {
+    println "neither fast nor slow"
     expect: true
   }
 }