## What changes were proposed in this pull request?
Updates links to the wiki to links to the new location of content on spark.apache.org.
## How was this patch tested?
Doc builds
Author: Sean Owen <sowen@cloudera.com>
Closes#15967 from srowen/SPARK-18073.1.
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.
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`.