Use colored/styled text output for diagnostics and usage info (#1775)

include/platform.hpp

@@ -28,6 +28,7 @@
 	#define STDERR_FILENO 2
 	#define ssize_t       int
 	#define SSIZE_MAX     INT_MAX
+	#define isatty        _isatty
 #else
 	#include <fcntl.h>  // IWYU pragma: export
 	#include <limits.h> // IWYU pragma: export

include/style.hpp

@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: MIT
+
+#ifndef RGBDS_STYLE_HPP
+#define RGBDS_STYLE_HPP
+
+#include <stdio.h>
+
+#if defined(_MSC_VER) || defined(__MINGW32__) || defined(__CYGWIN__)
+	#define STYLE_ANSI 0
+#else
+	#define STYLE_ANSI 1
+#endif
+
+enum StyleColor {
+#if STYLE_ANSI
+	// Values analogous to ANSI foreground and background SGR colors
+	STYLE_BLACK,
+	STYLE_RED,
+	STYLE_GREEN,
+	STYLE_YELLOW,
+	STYLE_BLUE,
+	STYLE_MAGENTA,
+	STYLE_CYAN,
+	STYLE_GRAY,
+#else
+	// Values analogous to `FOREGROUND_*` constants from `windows.h`
+	STYLE_BLACK,
+	STYLE_BLUE,    // bit 0
+	STYLE_GREEN,   // bit 1
+	STYLE_CYAN,    // STYLE_BLUE | STYLE_GREEN
+	STYLE_RED,     // bit 2
+	STYLE_MAGENTA, // STYLE_BLUE | STYLE_RED
+	STYLE_YELLOW,  // STYLE_GREEN | STYLE_RED
+	STYLE_GRAY,    // STYLE_BLUE | STYLE_GREEN | STYLE_RED
+#endif
+};
+
+void style_Enable(bool enable);
+void style_Set(FILE *file, StyleColor color, bool bold);
+void style_Reset(FILE *file);
+
+#endif // RGBDS_STYLE_HPP

include/usage.hpp

@@ -4,12 +4,14 @@
 #define RGBDS_USAGE_HPP
 
 #include <stdarg.h>
+#include <string>
+#include <utility>
+#include <vector>
 
-class Usage {
-	char const *usage;
-
-public:
-	Usage(char const *usage_) : usage(usage_) {}
+struct Usage {
+	std::string name;
+	std::vector<std::string> flags;
+	std::vector<std::pair<std::vector<std::string>, std::vector<std::string>>> options;
 
 	[[noreturn]]
 	void printAndExit(int code) const;