Add pyproject.toml

This also has the side effect of messing up my __main__; because
setuptools doesn't support __main__ modules, the entrypoints must refer
to a function.

Reference: pypa/setuptools#1995

mxmda/__main__.py

@@ -6,7 +6,17 @@
 from mxmda.app import command, parse_args
 from mxmda.errors import UserError
 
-if __name__ == '__main__':
+# https://github.com/pypa/setuptools/issues/1995
+# Proper solution specified in comment by @Xophmeister:
+# > In the current system, you have to delimit module and the
+# > entrypoint callable with a colon. What if the logic was
+# > something like:
+# >
+# > Split on:
+# >  If there are two components, then proceed as currently;
+# >  If there is only one component, then interpret this as
+# >  a direct module invocation?
+def issue_1995():
     logging.basicConfig(
         level=logging.INFO,
         format='%(asctime)s  [%(levelname)-8s] %(name)s: %(message)s',
@@ -18,3 +28,6 @@
     except UserError as exc:
         logging.getLogger(mxmda.__name__).error(exc)
         sys.exit(1)
+
+if __name__ == '__main__':
+    issue_1995()

pyproject.toml

@@ -0,0 +1,27 @@
+[project]
+name = "mxmda"
+version = "0.1.0"
+description = "Matrix Mail Delivery Agent"
+
+authors = [
+  { name="Olof Johansson", email="olof@ethup.se" },
+]
+
+readme = "README"
+requires-python = ">=3.6"
+
+dependencies = [
+  "matrix-nio[e2e]",
+  "PyYAML",
+  "requests",
+]
+
+[project.scripts]
+mxmda = "mxmda.__main__:issue_1995"
+
+[project.urls]
+"Homepage" = "https://github.com/olof/mxmda"
+"Bug Tracker" = "https://github.com/olof/mxmda/issues"
+
+[tool.setuptools]
+packages = ["mxmda"]