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/astronomy/.gitignore

@@ -0,0 +1 @@
+astronomy.py

source/python/astronomy/__init__.py

@@ -0,0 +1,7 @@
+# Astronomy Engine module initializer by Don Cross <cosinekitty@gmail.com>.
+
+# Pull Astronomy Engine's public symbols into module scope.
+from .astronomy import *
+
+# Delete the redundant nested module namespace.
+del astronomy