Also changed uses of "job" terminology to "application" when they
referred to an entire Spark program, to avoid confusion.

and new Python stuff

are now needed

Added checkpointing and fault-tolerance semantics to the programming guide. Fixed default checkpoint interval to being a multiple of slide duration. Fixed visibility of some classes and objects to clean up docs.

Also, adds a line in doc explaining how to use.

It's nicer if all the commands you need are made explicit.

Expand the PySpark programming guide.