Additional

This part is about functions not included in Libc or included in a different form.

The functions are grouped by functionality:

manipulate string	convert integer	iterate string	write to file descriptor
ft_substr	ft_itoa	ft_strmapi	ft_putchar_fd
ft_strjoin		ft_striteri	ft_putstr_fd
ft_strtrim			ft_putendl_fd
ft_split			ft_putnbr_fd