feat(cli): add --all option to run test command

challenges/is-palindrome/solutions/c/function/character.h

@@ -1,5 +1,5 @@
-#ifndef CHARACTER_H
-#define CHARACTER_H
+#ifndef __CHARACTER__
+#define __CHARACTER__
 
 /**
  * @brief Append a character to a string, assuming string points to an array
@@ -14,8 +14,8 @@ void character_append(char* string, char character);
  * @brief Converts the character to uppercase.
  *
  * @param character
- * @return const char
+ * @return char
  */
-const char character_to_upper(const char character);
+char character_to_upper(char character);
 
 #endif