Use #include "..." instead of #include <...> to include internal

[kmyk]

To include headers from other headers in the same library, we should use #include "...". This is a common manner (examples: 1, 2, 3).

However, the current AtCoder Library uses #include <...> (e.g. https://github.com/atcoder/ac-library/blob/114e690ade7fe839db3ea0e5f169207672ef0886/atcoder/all).
#include <...> is for headers in the standard system directories (see https://gcc.gnu.org/onlinedocs/cpp/Search-Path.html), but AtCoder Library is not system's one.

IIUC, if you use #include <...>, a problem will happen when multiple versions of the this library are installed.
For example, let say we have /usr/include/atcoder/segtree.hpp, /home/user/kimiyuki/GitHub/ac-library/atcoder/segtree.hpp, and /home/user/kimiyuki/GitHub/ac-library/atcoder/all. Under such situation, even when you include /home/user/kimiyuki/GitHub/ac-library/atcoder/all with #include "atcoder/all", this atcoder/all ignores /home/user/kimiyuki/GitHub/ac-library/atcoder/segtree.hpp and includes /usr/include/atcoder/segtree.hpp. This will cause mysterious bugs.

[kmyk]

BTW, the motivation of this issue is at online-judge-tools/verification-helper#345, which is an issue about the combination of our oj-bundle command and AtCoder Library.

[yosupo06]

Ah, your indication make sense. We don't have any strong opinion whether #include <...> or #include "...". We'll fix this.