Correct the file extension for voltdb/README.
Add a link to VoltDB DDL. Add some descriptions about the Map
Reduce in MongoDB.
Update README files for voltdb and mongodb-ruby:
- Add prerequisites, download Movie Lens and demo sections
  to voltdb/README
- Minor edits in mongodb-ruby/README
Update README for cassandra-cql3:
- Add download Movie Lens, start Cassandra, and load Movie Lens
  dataset sections.
Add comments to the DDLs for Cassandra CQL3 and VoltDB.
Update README:
- Add the copywright notice and license
- Add a link to the deleted Neo4J README
- Misc minor edits
Reformat the content of MIT License.
Add README and LICENSE (CC BY-NC 3.0) to the slides/ folder.