feat: add comments and define macros

libft.h

@@ -1,4 +1,35 @@
-int	ft_isalpha(const char c);
+#ifndef LIBFT_A
+#define LIBFT_A
+
+/*
+    The isalpha() function tests for
+    any character for which isupper(3) or
+    islower(3) is true.
+ */
+int	ft_isalpha(int c);
+/*
+    The ft_isdigit() function tests 
+    for a decimal digit character.  
+    Regardless of locale, this 
+    includes the following characters 
+    only: '0' '1' '2' '3' '4' '5' '6'
+    '7' '8' '9'
+ */
 int	ft_isdigit(int c);
+
+/*
+    The ft_isalnum() function tests 
+    for any character for which
+    isalpha(3) or isdigit(3) is true.
+ */
 int ft_isalnum(int c);
+
+/*  
+    The ft_isascii() function tests 
+    for an ASCII character, which is
+    any character between 0 and octal
+    0177 inclusive. 
+ */
 int	ft_isascii(int c);
+
+#endif