SlangResult and small bug/typos fixes (#448)

* Fixed some small typos in api-users-guide.md

* Fix some small typos in slang-test/main.cpp, render-test/render-d3d11.cpp

* Remove exit() calls from test code. Added Slang::Result, which works in the same way as COM HRESULT.

* FIx bug introduced when moving to Slang::Result - handling E_INVALIDARG on Dx11.

* Fix the testing of feature levels on Dx11 renderer.

* First attempt at README.md for slang-test.

* Tidied up the slang-test README.md file.

* Fix some small typos in tools/slang-test/main.cpp

* Fix spaces -> tabs problems.
Fix some small types.

1 files changed, 4 insertions, 2 deletions

diff --git a/tools/render-test/render.h b/tools/render-test/render.h
index 5eb0c967d..902067d62 100644
--- a/tools/render-test/render.h
+++ b/tools/render-test/render.h
@@ -5,6 +5,8 @@
 #include "window.h"
 #include "shader-input-layout.h"
 
+#include "../../source/core/slang-result.h"
+
 namespace renderer_test {
 
 typedef struct Buffer           Buffer;
@@ -90,14 +92,14 @@ enum class PrimitiveTopology
 class Renderer
 {
 public:
-    virtual void initialize(void* inWindowHandle) = 0;
+    virtual SlangResult initialize(void* inWindowHandle) = 0;
 
     virtual void setClearColor(float const* color) = 0;
     virtual void clearFrame() = 0;
 
     virtual void presentFrame() = 0;
 
-    virtual void captureScreenShot(char const* outputPath) = 0;
+    virtual SlangResult captureScreenShot(char const* outputPath) = 0;
     virtual void serializeOutput(BindingState * state, char const* outputPath) = 0;
     virtual Buffer* createBuffer(BufferDesc const& desc) = 0;