Add support for nested key schemas
Add support for nested key schemas

If the field defines a key schema, add any fields from the nested
schema prefixed by the field name and a * to denote the wildcard.

See also: https://github.com/nicolaiarocci/cerberus/pull/36

charlesflynn/eve-docs,hermannsblum/eve-docs,hermannsblum/eve-docs,rs/eve-docs