Also warns if spark.cleaner.ttl is not set in the version where you pass
your own SparkContext.

ordering, so the reduce function must also be commutative.

Made StorageLevel constructor private, and added StorageLevels.create() to the Java API. Updates scala and java programming guides.

- Edited quick start and tuning guide to simplify them a little
- Simplified top menu bar
- Made private a SparkContext constructor parameter that was left as
  public
- Various small fixes

also adding the version to the navbar so it is easy to tell which
version of Spark these docs were compiled for.

throughout the docs: SPARK_VERSION, SCALA_VERSION, and MESOS_VERSION.

To use them, e.g. use {{site.SPARK_VERSION}}.

Also removes uses of {{HOME_PATH}} which were being resolved to ""
by the templating system anyway.

- Rework/expand the nav bar with more of the docs site
- Removing parts of docs about EC2 and Mesos that differentiate between
  running 0.5 and before
    - Merged subheadings from running-on-amazon-ec2.html that are still relevant
      (i.e., "Using a newer version of Spark" and "Accessing Data in S3") into
      ec2-scripts.html and deleted running-on-amazon-ec2.html
- Added some TODO comments to a few docs
- Updated the blurb about AMP Camp
- Renamed programming-guide to spark-programming-guide
- Fixing typos/etc. in Standalone Spark doc

easier to read.

which can be compiled via jekyll, using the command `jekyll`. To compile
and run a local webserver to serve the doc as a website, run
`jekyll --server`.