Switch to pyproject.toml over setup.py

pyproject.toml

@@ -0,0 +1,40 @@
+[build-system]
+requires = ["flit_core >=3.2,<4"]
+build-backend = "flit_core.buildapi"
+
+[project]
+name = "idna"
+description = "Internationalized Domain Names in Applications (IDNA)"
+readme = "README.rst"
+authors = [
+  {name = "Kim Davies", email = "kim@cynosure.com.au"}
+]
+classifiers = [
+  "Development Status :: 5 - Production/Stable",
+  "Intended Audience :: Developers",
+  "Intended Audience :: System Administrators",
+  "License :: OSI Approved :: BSD License",
+  "Operating System :: OS Independent",
+  "Programming Language :: Python",
+  "Programming Language :: Python :: 3",
+  "Programming Language :: Python :: 3 :: Only",
+  "Programming Language :: Python :: 3.5",
+  "Programming Language :: Python :: 3.6",
+  "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",
+  "Programming Language :: Python :: Implementation :: CPython",
+  "Programming Language :: Python :: Implementation :: PyPy",
+  "Topic :: Internet :: Name Service (DNS)",
+  "Topic :: Software Development :: Libraries :: Python Modules",
+  "Topic :: Utilities",
+]
+requires-python = ">=3.5"
+dynamic = ["version"]
+
+[project.urls]
+"Source" = "https://github.com/kjd/idna"
+"Changelog" = "https://github.com/kjd/idna/blob/master/HISTORY.rst"
+"Issue tracker" = "https://github.com/kjd/idna/issues"