Add tomli as vendorised dependency

This eventually will allow reading project metadata directly from
`pyproject.toml`

setuptools/_vendor/tomli/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 Taneli Hukkinen
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

setuptools/_vendor/tomli/__init__.py

@@ -0,0 +1,9 @@
+"""A lil' TOML parser."""
+
+__all__ = ("loads", "load", "TOMLDecodeError")
+__version__ = "1.2.3"  # DO NOT EDIT THIS LINE MANUALLY. LET bump2version UTILITY DO IT
+
+from tomli._parser import TOMLDecodeError, load, loads
+
+# Pretend this exception was created here.
+TOMLDecodeError.__module__ = "tomli"