Added MapEntries' contexts and updated SPI documentation

src/main/java/net/openhft/chronicle/map/MapContext.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2015 Higher Frequency Trading
+ *
+ *  http://www.higherfrequencytrading.com
+ *  
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *  
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *  
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package net.openhft.chronicle.map;
+
+import net.openhft.chronicle.hash.HashContext;
+
+/**
+ * Context, in which {@link MapEntry MapEntries} are accessed.
+ * 
+ * @param <K> the key type of accessed {@link ChronicleMap}
+ * @param <V> the value type of accessed {@code ChronicleMap}
+ */
+public interface MapContext<K, V> extends HashContext<K> {
+    /**
+     * Returns the accessed {@code ChronicleMap}.
+     */
+    @Override
+    ChronicleMap<K, V> hash();
+
+    /**
+     * Synonym to {@link #hash()}.
+     */
+    ChronicleMap<K, V> map();
+}