Adding hoodie-spark to support Spark Datasource for Hoodie

- Write with COW/MOR paths work fully
 - Read with RO view works on both storages*
 - Incremental view supported on COW
 - Refactored out HoodieReadClient methods, to just contain key based access
 - HoodieDataSourceHelpers class can be now used to construct inputs to datasource
 - Tests in hoodie-client using new helpers and mechanisms
 - Basic tests around save modes & insert/upserts (more to follow)
 - Bumped up scala to 2.11, since 2.10 is deprecated & complains with scalatest
 - Updated documentation to describe usage
 - New sample app written using the DataSource API

hoodie-spark/src/main/java/com/uber/hoodie/KeyGenerator.java

@@ -0,0 +1,47 @@
+/*
+ *  Copyright (c) 2017 Uber Technologies, Inc. (hoodie-dev-group@uber.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 com.uber.hoodie;
+
+import com.uber.hoodie.common.model.HoodieKey;
+
+import org.apache.avro.generic.GenericRecord;
+import org.apache.commons.configuration.PropertiesConfiguration;
+
+import java.io.Serializable;
+
+/**
+ * Abstract class to extend for plugging in extraction of {@link com.uber.hoodie.common.model.HoodieKey}
+ * from an Avro record
+ */
+public abstract class KeyGenerator implements Serializable {
+
+    protected transient PropertiesConfiguration config;
+
+    protected KeyGenerator(PropertiesConfiguration config) {
+        this.config = config;
+    }
+
+    /**
+     * Generate a Hoodie Key out of provided generic record.
+     *
+     * @param record
+     * @return
+     */
+    public abstract HoodieKey getKey(GenericRecord record);
+}