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

CMakeLists.txt

@@ -26,10 +26,10 @@ foreach(ver ${pybind11_version_defines})
   endif()
 endforeach()
 
-if(PYBIND11_VERSION_PATCH MATCHES [[([a-zA-Z]+)]])
+if(PYBIND11_VERSION_PATCH MATCHES [[\.([a-zA-Z0-9]+)$]])
   set(pybind11_VERSION_TYPE "${CMAKE_MATCH_1}")
 endif()
-string(REGEX MATCH "[0-9]+" PYBIND11_VERSION_PATCH "${PYBIND11_VERSION_PATCH}")
+string(REGEX MATCH "^[0-9]+" PYBIND11_VERSION_PATCH "${PYBIND11_VERSION_PATCH}")
 
 project(
   pybind11