Exclude some private modules in epydoc
Add missing license headers found with RAT
Some doc improvements

- List higher-level projects that run on Spark
- Tweak CSS
Add Apache incubator notice to README
Updated LICENSE with third-party licenses
Merge pull request #887 from mateiz/misc-fixes

Miscellaneous fixes for 0.8
Add Apache parent POM
SPARK-884: Add unit test to validate Spark json output