feat: add ft_toupper function

ft_toupper.c

@@ -0,0 +1,8 @@
+#include "libft.h"
+
+int	ft_toupper(int c)
+{
+	if ('a' <= c && c <= 'z')
+		c -= 32;
+	return (c);
+}

libft.h

@@ -88,4 +88,13 @@ void	*ft_memmove(void *dst, const void *src, size_t n);
 */
 size_t	ft_strlcpy(char *dst, const char *src, size_t dstsize);
 
+// size_t	ft_strlcat(char *dst, const char *src, size_t dstsize);
+
+/*
+	The toupper() function converts a 
+	lower-case letter to the 
+	corresponding upper-case letter.
+*/
+int	ft_toupper(int c);
+
 #endif