Add tests and fix minor problems in specifier parser

include/simple-printf/simple-printf.h

@@ -2,16 +2,44 @@
 #define _SIMPLE_PRINTF_H_
 
 #include <stddef.h>
+#include <stdbool.h>
 
 #ifndef SIMPLE_PRINTF_ATTR_FORMAT
-#   if ((__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)))
-#       define SIMPLE_PRINTF_ATTR_FORMAT(fmt, args) __attribute__((__format__(__printf__, fmt, args)))
-#   else
-#       define SIMPLE_PRINTF_ATTR_FORMAT(fmt, args)
-#   endif
+#if ((__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)))
+#define SIMPLE_PRINTF_ATTR_FORMAT(fmt, args) __attribute__((__format__(__printf__, fmt, args)))
 #else
-#   define SIMPLE_PRINTF_ATTR_FORMAT(fmt, args)
+#define SIMPLE_PRINTF_ATTR_FORMAT(fmt, args)
 #endif
+#else
+#define SIMPLE_PRINTF_ATTR_FORMAT(fmt, args)
+#endif
+
+enum format_specifier_type {
+	FMT_INVALID = 0,
+	FMT_INTEGER,
+	FMT_UNSIGNED,
+	FMT_STRING,
+	FMT_HEXUINT_CAPITALIZED,
+	FMT_HEXUINT,
+	FMT_CHAR,
+	FMT_SIZE,
+	FMT_PERCENT,
+};
+
+struct format_specifier {
+	enum format_specifier_type specifier;
+	size_t length; /**< @brief lenght of formatted output.*/
+	bool zero_pad;
+	size_t length_of_provided_specifier;
+};
+
+/**
+ * @brief Helper function to parse printf format specifiers
+ * 
+ * @param start Start of parsing
+ * @param[out] result Result of format specifier parsing
+ */
+void parse_format_specifier(const char *start, struct format_specifier *result);
 
 /**
  * @brief Simple implementation of snprintf