Improving Makefile, merging work for C-42sh

Changes :

General:
Moving srcs/ files to sources/ .

Makefile :
Add rules, Flags, change names add a directory for objects files.

Sources/ :
ft_mem_malloc.c, sources/ft_lst_list_to_str.c
Add files from C-42sh version.

includes/libsimpleslist.h
Change name to fit with repository name.