Refactor warnings and errors (#1728)

* Remove `err` and `warn`, keep `errx` and `warnx`, using them in RGBGFX too

* Separate RGBGFX and RGBLINK warnings/errors from main options

* Separate `report` function into `error` and `fatal` messages

* Implicit newlines for most RGBASM errors

src/link/script.y

@@ -30,6 +30,7 @@
 
 	#include "link/main.hpp"
 	#include "link/section.hpp"
+	#include "link/warning.hpp"
 
 	using namespace std::literals;