RegEx re-implemented as a module

Re-wrote nrex as a module using godot-specific parts and new
features:

 * Added string substitutions.
 * Named groups are now supported.
 * Removed use of mutable variables in RegEx. RegExMatch is returned
   instead.

drivers/SCsub

@@ -25,7 +25,6 @@ SConscript('gl_context/SCsub');
 
 # Core dependencies
 SConscript("png/SCsub");
-SConscript("nrex/SCsub");
 
 # Tools override
 # FIXME: Should likely be integrated in the tools/ codebase