Add 'simple' concept to URI types
Add 'simple' concept to URI types

Summary: Replacing 'valid', to account for potential escaping support (usually %-encoding).

Reviewed By: joshkehn

Differential Revision: D36926575

fbshipit-source-id: e87a98427577c8599b9af5e0d2f1d4fdeba1542e

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift