Hide private symbols in Python package.

I realized that the way I structured the pip package
in version 2.0.15 made the private symbols (those whose
names begin with an underscore) to be visible by the importer.
I reworked the package structure so this no longer happens.

This is now fixed in:
https://pypi.org/project/astronomy-engine/2.0.16/

source/python/publish

@@ -1,7 +1,6 @@
 #!/bin/bash
-mkdir -pv astronomy || exit $?
-rm -f dist/* astronomy/*
-cp -v astronomy.py astronomy/__init__.py || exit $?
+rm -f dist/*
+cp -v astronomy.py astronomy/astronomy.py || exit $?
 python3 -m build || exit $?
 python3 -m twine upload --repository astronomy-engine dist/* || exit $?
 exit 0