Add configuration system for core renderdoc module

* This allows persistent config storage and registering tweak variables that
  works independent of the UI's configuration.
* Config vars can be debug only, which means they will be compiled out in stable
  version releases. This allows for debug-logging tweaks that are available in
  all builds (including nightly builds) for diagnostic purposes, but have zero
  overhead in stable releases.
* Variables have a loose hierarchy defined with _ or . to separate nodes.

renderdoc/core/core.cpp

@@ -454,6 +454,8 @@ void RenderDoc::Initialise()
   // information to stdout/stderr and being piped around and processed!
   if(IsReplayApp())
     RDCLOGOUTPUT();
+
+  ProcessConfig();
 }
 
 RenderDoc::~RenderDoc()
@@ -494,6 +496,8 @@ RenderDoc::~RenderDoc()
     m_RemoteThread = 0;
   }
 
+  delete m_Config;
+
   Process::Shutdown();
 
   Network::Shutdown();