Replace build system with flit

pyproject.toml

@@ -0,0 +1,68 @@
+[project]
+name = "Willow"
+description = "A Python image library that sits on top of Pillow, Wand and OpenCV"
+authors = [{name = "Karl Hobley", email = "[email protected]"}]
+readme = "README.rst"
+license = {file = "LICENSE"}
+keywords = ["Imaging"]
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Topic :: Multimedia :: Graphics",
+    "Topic :: Multimedia :: Graphics :: Graphics Conversion",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: BSD License",
+    "Operating System :: OS Independent",
+    "Programming Language :: Python",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3 :: Only",
+    "Programming Language :: Python :: 3.7",
+    "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+]
+
+dynamic = ["version"]  # will read __version__ from willow/__init__.py
+requires-python = ">=3.7"
+dependencies = [
+    "filetype>=1.0.10,!=1.1.0",
+    "defusedxml>=0.7,<1.0",
+]
+
+[project.optional-dependencies]
+testing = [
+    "Pillow>=9.1.0,<11.0.0",
+    "Wand>=0.6,<1.0",
+    "mock>=3.0,<4.0",
+    "pillow-heif>=0.7.0,<1.0.0",
+    "black==22.3.0",
+    "ruff==0.0.275",
+]
+
+[project.urls]
+Source = "https://github.com/wagtail/Willow"
+Changelog = "https://github.com/wagtail/Willow/blob/main/CHANGELOG.txt"
+
+
+[build-system]
+requires = ["flit_core >=3.2,<4"]
+build-backend = "flit_core.buildapi"
+
+[tool.flit.module]
+name = "willow"
+
+[tool.flit.sdist]
+exclude = [
+    ".*",
+    "*.json",
+    "*.ini",
+    "*.sh",
+    "*.yml",
+    "*.yaml",
+    "docs/",
+    "tests/",
+    "CHANGELOG.txt",
+    "Dockerfile.py3",
+    "ruff.toml",
+    "runtests.py",
+]