feat: setup.py redesign and helpers (#2433)

* feat: setup.py redesign and helpers

* refactor: simpler design with two outputs

* refactor: helper file update and Windows support

* fix: review points from @YannickJadoul

* refactor: fixes to naming and more docs

* feat: more customization points

* feat: add entry point pybind11-config

* refactor: Try Extension-focused method

* refactor: rename alt/inplace to global

* fix: allow usage with git modules, better docs

* feat: global as an extra (@YannickJadoul's suggestion)

* feat: single version location

* fix: remove the requirement that setuptools must be imported first

* fix: some review points from @wjacob

* fix: use .in, add procedure to docs

* refactor: avoid monkeypatch copy

* docs: minor typos corrected

* fix: minor points from @YannickJadoul

* fix: typo on Windows C++ mode

* fix: MSVC 15 update 3+ have c++14 flag

See <https://docs.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=vs-2019>

* docs: discuss making SDists by hand

* ci: use pep517.build instead of manual setup.py

* refactor: more comments from @YannickJadoul

* docs: updates from @ktbarrett

* fix: change to newly recommended tool instead of pep517.build

This was intended as a proof of concept; build seems to be the correct replacement.

See https://github.com/pypa/pep517/pull/83

* docs: updates from @wjakob

* refactor: dual version locations

* docs: typo spotted by @wjakob

.github/workflows/format.yml

@@ -1,3 +1,6 @@
+# This is a format job. Pre-commit has a first-party GitHub action, so we use
+# that: https://github.com/pre-commit/action
+
 name: Format
 
 on:
@@ -17,6 +20,9 @@ jobs:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2
     - uses: pre-commit/action@v2.0.0
+      with:
+        # Slow hooks are marked with manual - slow is okay here, run them too
+        extra_args: --hook-stage manual
 
   clang-tidy:
     name: Clang-Tidy