Package docs

This is a few changes based on the original patch by @scrapcodes.

Author: Prashant Sharma <prashant.s@imaginea.com>
Author: Patrick Wendell <pwendell@gmail.com>

Closes #785 from pwendell/package-docs and squashes the following commits:

c32b731 [Patrick Wendell] Changes based on Prashant's patch
c0463d3 [Prashant Sharma] added eof new line
ce8bf73 [Prashant Sharma] Added eof new line to all files.
4c35f2e [Prashant Sharma] SPARK-1563 Add package-info.java and package.scala files for all packages that appear in docs
(cherry picked from commit 46324279dae2fa803267d788f7c56b0ed643b4c8)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>