Address concerns in 5473393e30 (RL interface)

Fixes 5473393e30.

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
This was SVN commit r24631.

source/scriptinterface/ScriptEngine.h

@@ -23,6 +23,8 @@
 
 #include "js/Initialization.h"
 
+#include <list>
+
 /**
  * A class using the RAII (Resource Acquisition Is Initialization) idiom to manage initialization
  * and shutdown of the SpiderMonkey script engine. It also keeps a count of active script contexts