Idea: mention 3rd party "extended stdlib" modules in developer guide

We have a section in the developer guide specifically on proposing changes to the standard library: http://cpython-devguide.readthedocs.io/en/latest/stdlibchanges.html

One of the alternatives to standard library additions that frequently needs to be brought up on python-ideas is the possibility of adding to one of the "stdlib enhancement" projects that adds assorted general purpose programming utilities that are nevertheless considered sufficiently niche use cases that they don't make the cut for standard library inclusion (or, alternatively, folks want them now, rather than having to wait for a new CPython feature release)

Perhaps it would make sense to specifically mention some of those projects in this part of the developer guide? The main two that come to mind are:

• boltons: https://boltons.readthedocs.io/
• more-itertools: https://pypi.python.org/pypi/more-itertools/

There are probably others, but once we start the list, it's relatively easy to add new entries, but with no list at all, it's unlike anyone (else) would suggest adding one.

stdlibchanges.html にある開発者ガイドの標準ライブラリの変更に関するセクションから始め、代替プロジェクトが現在どのように説明されているかを確認してください。セクションの既存のスタイルを維持しながら、boltons と more-itertools への言及を追加してください。ガイドが読者を標準ライブラリへの追加の代替としてこれらのプロジェクトに案内できれば完了です。