[build] Add minimal `pyproject.toml`

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ['setuptools']
+build-backend = 'setuptools.build_meta'

setup.py

@@ -1,8 +1,12 @@
 #!/usr/bin/env python3
 
-import os.path
+# Allow execution from anywhere
-import subprocess
+import os
 import sys
+
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+
+import subprocess
 import warnings
 
 try: