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.
1. Slight change in organization 2. Added pre-requisites 3. Made a new section about determining memory footprint of an RDD 4. Other small changes