Address concerns in rP23917 (RL interface)

Fixes rP23917.

This:

• Puts RL code under the RL namespace to avoid name collisions
• Avoids usage of new/delete
• Adds more documentation
• Does general cleanup (const-correctness, move semantics, argument types, early returns...)

Patch by: irishninja

Comments by: Vladislavbelov, wraitii

Differential Revision: https://code.wildfiregames.com/D2947