DATAKV-101 - Favor Iterable over Collection types for KeyValueOperations.

Change return types for Adapter and Operations from Collection types to Iterable. Added count(keyspace) to KeyValueAdapter.

Original pull request: #8.

src/main/java/org/springframework/data/map/MapKeyValueAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -104,6 +104,15 @@ public class MapKeyValueAdapter extends AbstractKeyValueAdapter {
 		return get(id, keyspace) != null;
 	}
 
+
+	/* (non-Javadoc)
+	 * @see org.springframework.data.keyvalue.core.KeyValueAdapter#count(java.io.Serializable)
+	 */
+	@Override
+	public long count(Serializable keyspace) {
+		return getKeySpaceMap(keyspace).size();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.keyvalue.core.KeyValueAdapter#get(java.io.Serializable, java.io.Serializable)