Add Python API.
Bundle cloudpickle with pyspark.
Use only cPickle for serialization in Python API.

Objects serialized with JSON can be compared for equality, but JSON can be slow
to serialize and only supports a limited range of data types.
Use numpy in Python k-means example.
Fix options parsing in Python pi example.
Refactor Python MappedRDD to use iterator pipelines.
Implement fold() in Python API.
Add broadcast variables to Python API.
Add mapPartitions(), glom(), countByValue() to Python API.
Add countByKey(), reduceByKeyLocally() to Python API
Use local combiners in Python API combineByKey().
Simplify Python worker; pipeline the map step of partitionBy().
Add pipe(), saveAsTextFile(), sc.union() to Python API.
Fix minor bugs in Python API examples.
Fix Python 2.6 compatibility in Python API.
Updated Kryo to 2.20.
Merge tag 'v0.6.0' into python-api
Update Python API for v0.6.0 compatibility.
Add PySpark README and run scripts.
Remove PYTHONPATH from SparkContext's executorEnvs.

It makes more sense to pass it in the dictionary
of environment variables that is used to construct
PythonRDD.