Vulkan triangle!

Switched to Vulkan 1.1 GLSL dialect
Added vulkan test shader
Implemented test render thread function

standard_assets/shaders/vulkan_test.frag

@@ -0,0 +1,12 @@
+#version 450
+
+// Temporary test shader for vulkan bringup...
+// See https://vulkan-tutorial.com/Drawing_a_triangle/Graphics_pipeline_basics/Shader_modules
+
+layout(location = 0) in vec3 fragColor;
+
+layout(location = 0) out vec4 outColor;
+
+void main() {
+    outColor = vec4(fragColor, 1.0);
+}