Python: make package PEP-561 compliant (#94)

* Python: convert to package

This will allow to ship e.g. the py.typed file in the distribution.

* Python: make package PEP-561 compliant

The code already has type annotations. Let's ship the py.typed
file so the typing information actually can be consumed by e.g. mypy

Author: Carbenium

src/python/psychrolib.py src/python/psychrolib/__init__.pysrc/python/psychrolib.py renamed to src/python/psychrolib/__init__.py

@@ -12,5 +12,6 @@
       license='MIT',
       platforms = ['Windows', 'Linux', 'Solaris', 'Mac OS-X', 'Unix'],
       python_requires='>=3.6',
-      py_modules=['psychrolib'],
-     )
+      packages=['psychrolib'],
+      package_data={'psychrolib': ['py.typed']},
+     )