Use the oldest-supported-numpy meta package

python/pyproject.toml

@@ -2,6 +2,6 @@
 requires = [
     "setuptools>=42",
     "wheel",
-    "numpy>=1.17.3"
+    "oldest-supported-numpy"
 ]
 build-backend = "setuptools.build_meta"

python/setup.py

@@ -71,5 +71,7 @@ setup(name             = MODULE_NAME,
          "Operating System :: MacOS"
       ],
       python_requires = ">=3.0",
-      install_requires = ["numpy>=1.17.3"]
+      # The ABI incompatibility of numpy is a pain, for now set the 
+      # min numpy version such that we have wheels for CPython 3.5 & 3.6
+      install_requires = ["numpy>=1.13.3"]
       )