fix: packaged data still wrong

MANIFEST.in

@@ -0,0 +1 @@
+include ext_src/*

setup.py

@@ -4,12 +4,13 @@ from Cython.Build import cythonize
 extensions = [
     Extension(
         "sphereproj._project",
-        [
-            "ext_src/_project.pyx",
+        sources=[
+            "ext_src/_project.pyx", "ext_src/_project.cpp"
         ],
+        include_dirs=["ext_src"],
         language="c++"
     )
 ]
 
 
-setup(py_modules=["sphereproj"],ext_modules=cythonize(extensions))
+setup(ext_modules=cythonize(extensions))

src/sphereproj/__init__.py

@@ -0,0 +1 @@
+from ._project import spherical_projection