Expand documentation for 'slice'
Changes based on review comments
Mention that migration is for major releases
Updates based on review
Fixes #280
Merge branch 'issue-280-slice'
Merge pull request #324 from rethinkdb/michel_267_migration

Mention that migration is for major releases
Adding new images
Adding/updating images
Add quickstart image
Moving holding hands illustration to 'start a cluster' page. It didn't quite fit the 30 second tutorial (and had style problems because of code block overlap).
Merge pull request #333 from rethinkdb/slava_moving_illustration

Moving holding hands illustration to 'start a cluster' page.
fixing typo 'exmple'
Merge pull request #341 from rethinkdb/grey_example_typo_fix

Fixing 'exmple' typo
Make gen_python.py Python 3 compatible
Associate the grouped_stream type with RqlQuery
Apply the explicit label of "slice"