Add string-based renderer backend configuration

Rather than using integer-indices, just use plaintext case-insensitive
names and leave the actual enum indexes as an implementation detail.

include/renderer.hpp

@@ -12,6 +12,9 @@ enum class RendererType : s8 {
 	OpenGL = 1,
 };
 
+std::optional<RendererType> fromString(std::string inString);
+const char* toString(RendererType rendererType);
+
 class GPU;
 
 class Renderer {