TODO first
cp parse_git_index.c cmd_ls_files.c
create Makefile
ignore binary executable file
simple separate compliation
refactor
refactor
add minigit.h in the dependency list
deprecate old function ls_files
concate minigit.h
add minigit.h in the dependency list
refactor
eliminate header.h
refactor
refactor
refactor
use .git/index when argv is omitted
DRY
successfully integrated new cmd_ls_files
rename