Description for the functions used in the printf project

printf - prints a formatted string write_character - prints a character, called by %c and %% write_string - funtion that writes a string, called by %s print_binary - function that prints a unsigned integer in binary, called by %b _strlen - a function that finds the length of string print_reverse - function that prints a string in reverse, called by %s print_number - function that prints a singed integer, called by %d and %i is_in - function that checks for the membership of a character in an array of characters. we use this to select specifiers.