chore: Moved from setuptools to flit as the build-system.

Setuptools started to misbehave when switching to pyproject.toml and dumped way to many files into the sdist archive, contradicting its own documentation. Flit is way faster, needs less configuration, and just works.

pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
-requires = ["setuptools>=61.0"]
-build-backend = "setuptools.build_meta"
+requires = ["flit_core >=3.9,<4"]
+build-backend = "flit_core.buildapi"
 
 [project]
 name = "bottle"
@@ -50,12 +50,12 @@ Changelog = "https://bottlepy.org/docs/dev/changelog.html"
 [project.scripts]
 "bottle.py" = "bottle:main"
 
-[tool.setuptools]
-py-modules = ["bottle"]
-platforms = ["any"]
-
-[tool.setuptools.dynamic]
-version = {attr = "bottle.__version__"}
+[tool.flit.sdist]
+include = [
+  "test/*.py",
+  "test/views/*.tpl",
+  "AUTHORS"
+]
 
 [tool.pytest.ini_options]
 addopts = "-ra"