Make comments more consistent

- Changes most `/* comments */` to `// comments`
- Changes `/**` block comments consistently to `/*`
- Adds consistent license comments to all files

Also renames `T_POP_SET` to `T_Z80_SET`

include/asm/macro.h

@@ -34,4 +34,4 @@ uint32_t macro_UseNewUniqueID(void);
 void macro_ShiftCurrentArgs(int32_t count);
 uint32_t macro_NbArgs(void);
 
-#endif
+#endif // RGBDS_MACRO_H