performance improvement - getCurrentContext

inlined getCurrentContext and getMutableContext
Further work on #1086.
Brings test from 0m37.913 to 0m25.584s
Catch2 is now faster than Catch 1.x!!

include/internal/catch_context.cpp

@@ -45,21 +45,16 @@ namespace Catch {
         IResultCapture* m_resultCapture = nullptr;
     };
 
-    namespace {
-        Context* currentContext = nullptr;
-    }
-    IMutableContext& getCurrentMutableContext() {
-        if( !currentContext )
-            currentContext = new Context();
-        return *currentContext;
-    }
-    IContext& getCurrentContext() {
-        return getCurrentMutableContext();
+    IMutableContext *IMutableContext::currentContext = nullptr;
+
+    void IMutableContext::createContext()
+    {
+        currentContext = new Context();
     }
 
     void cleanUpContext() {
-        delete currentContext;
-        currentContext = nullptr;
+        delete IMutableContext::currentContext;
+        IMutableContext::currentContext = nullptr;
     }
     IContext::~IContext() = default;
     IMutableContext::~IMutableContext() = default;

include/internal/catch_context.h

@@ -15,6 +15,7 @@ namespace Catch {
     struct IResultCapture;
     struct IRunner;
     struct IConfig;
+    struct IMutableContext;
 
     using IConfigPtr = std::shared_ptr<IConfig const>;
 
@@ -33,10 +34,26 @@ namespace Catch {
         virtual void setResultCapture( IResultCapture* resultCapture ) = 0;
         virtual void setRunner( IRunner* runner ) = 0;
         virtual void setConfig( IConfigPtr const& config ) = 0;
+
+    private:
+        static IMutableContext *currentContext;
+        friend IMutableContext& getCurrentMutableContext();
+        friend void cleanUpContext();
+        static void createContext();
     };
 
-    IContext& getCurrentContext();
-    IMutableContext& getCurrentMutableContext();
+    inline IMutableContext& getCurrentMutableContext()
+    {
+        if( !IMutableContext::currentContext )
+            IMutableContext::createContext();
+        return *IMutableContext::currentContext;
+    }
+
+    inline IContext& getCurrentContext()
+    {
+        return getCurrentMutableContext();
+    }
+
     void cleanUpContext();
 }