- substr if start > str length
- all list functions check for NULL reference
- not modifying const pointers

bonus rule in Makefile remove guard close in libft.h
to declare t_list struct and ft_lst* prototypes.
Fixed ft_lstclear with recursion.

- Normed libf.h
- Removed ugly conditions in ft_strnstr

- bonus rule to add the *_bonus files to libft.a
- normed memmove, calloc and bonus

- memmove doesnt depend on a buffer size
- calloc return NULL if count or size == 0
- added byte type

Created a few dummy functions to resolve functions
having more than 25 lines.