CDK-360. DatasetKeyOutputFormat creates orphan directories.
Add line about new MapReduce support for Datasets.
CDK-362. Dataset example is failing with 'org.apache.hadoop.ipc.RemoteException: Server IPC version 7 cannot communicate with client version 4'
performance enhancement
CDK-323: Consolidate FS writer code in FileSystemWriter.

This introduces FileSystemWriter, which consolidates the boilerplate
code from the parquet and avro writers by wrapping an internal
FileAppender API. This is mirrors the DatasetWriter API, but allows
implementations to throw IOExceptions and assume that the read or write
state is correctly enforced in the FileSystemWriter. The new writer
handles state, logging, and IOExceptions. It also removes the need for
FileSystemWriters by handling format-appender resolution internally.

The old writers have been renamed to AvroAppender and ParquetAppender
and are now focused on only the format code.
CDK-323: Discard empty files.

This fixes CDK-323 by tracking how many events are written and
discarding 0-event files. Test added in TestFileSystemWriters.
Set property vers.hadoop-deps to release version 0.12.0.
Remove Hadoop 1 modules during release, since the new generated artifact
coordinates are not unique.
[maven-release-plugin] prepare release release-0.12.0
[maven-release-plugin] prepare for next development iteration
Update jdiff files.
Update hadoop-1 dependency versions after 0.12.0 release.

These are for testing only, so it's okay that the release tag doesn't
have the right version.
cleanup visibility
CDK-365: Shut down HBase and DFS clusters to fix conflicts.
CDK-365: Add test dependency on thrift 0.9.0.

There is a conflict between the thrift dependency from hbase (0.8.0) in
hadoop-1 and the version from hive (0.9.0). This adds a test dependency
on 0.9.0 that fixes the conflict and allows Travis CI tests to pass.
Long-term, we need to deconflict the hadoop-1 dependencies.
minor performance enhancements
Remove warning for duplicate sources in PartitionStrategy.

Source fields can be used more than once.
Add descriptor validation for partition strategy.
Allow partition names to duplicate field names, add test.

This updates the warning in the PartitionStrategy builder so that it
does not catch when partition names duplicate source names from the
schema. This is a common practice in HBase, where the key is actually
used to store the value for some fields.
CDK-153: Add tests for generated Hive partitions.