The beginning of rewriting "git add -i" in C.
* js/builtin-add-i:
built-in add -i: implement the `help` command
built-in add -i: use color in the main loop
built-in add -i: support `?` (prompt help)
built-in add -i: show unique prefixes of the commands
built-in add -i: implement the main loop
built-in add -i: color the header in the `status` command
built-in add -i: implement the `status` command
diff: export diffstat interface
Start to implement a built-in version of `git add --interactive`
f7998d9793