Minor documentation and style fixes for PySpark.

core/src/main/scala/spark/api/python/PythonPartitioner.scala

core/src/main/scala/spark/api/python/PythonRDD.scala

docs/index.md

docs/python-programming-guide.md

pyspark/examples/kmeans.py

pyspark/examples/logistic_regression.py

pyspark/examples/pi.py

pyspark/examples/transitive_closure.py

pyspark/examples/wordcount.py

pyspark/pyspark/__init__.py