refactor: identifiers in a file (#511)

* refactor: identifiers in a file

* chore: more typing

* refactor: PlatStr -> PlatformName

* refactor: load in file, use importlib.resources

* refactor: change toml structure

* refactor: use common Traversable

* fix: ensure reasonable version of importlib_resources

* style: fix extra line

setup.cfg

@@ -32,6 +32,7 @@ install_requires =
     toml
     certifi
     typing_extensions; python_version < '3.8'
+    importlib_resources>=1.4; python_version < '3.9'
 
 [options.package_data]
 cibuildwheel = resources/*
@@ -112,6 +113,10 @@ ignore_missing_imports = True
 [mypy-bashlex.*]
 ignore_missing_imports = True
 
+# Has type stubs, but no pyproject.toml or .pyi files in the wheel.
+[mypy-toml.*]
+ignore_missing_imports = True
+
 [tool:isort]
 profile=black
 multi_line_output=3