Resolve "Descriptor in multiple shader stages"

Closes #76 (closed)

include/vkcv/ShaderStage.hpp

 #pragma once
 
 namespace vkcv {
-	
-	enum class ShaderStage
+
+	enum class ShaderStage : VkShaderStageFlags
 	{
-		VERTEX,
-		TESS_CONTROL,
-		TESS_EVAL,
-		GEOMETRY,
-		FRAGMENT,
-		COMPUTE
+		VERTEX = VK_SHADER_STAGE_VERTEX_BIT,
+		TESS_CONTROL = VK_SHADER_STAGE_TESSELLATION_CONTROL_BIT,
+		TESS_EVAL = VK_SHADER_STAGE_TESSELLATION_EVALUATION_BIT,
+		GEOMETRY = VK_SHADER_STAGE_GEOMETRY_BIT,
+		FRAGMENT = VK_SHADER_STAGE_FRAGMENT_BIT,
+		COMPUTE = VK_SHADER_STAGE_COMPUTE_BIT
 	};
 
+	using ShaderStages = vk::Flags<ShaderStage>;
 }