Riak Search Doc (2.0.0)

Added schema doc, removed legacies. I also snuck in a CSS code layout patch.

Whoever reviews this, it might be easier to take a look at the complete rendered files.

https://github.com/basho/basho_docs/blob/feature/er/yokozuna-docs/source/languages/en/riak/dev/using/search.md

https://github.com/basho/basho_docs/blob/feature/er/yokozuna-docs/source/languages/en/riak/dev/advanced/search.md

https://github.com/basho/basho_docs/blob/feature/er/yokozuna-docs/source/languages/en/riak/dev/advanced/search-schema.md