python: Implement main module

This commit implements the python main cli module. Currently it supports
a preliminary set of command line options but should be able to
successfully generate passwords.

python/passgeny/meson.build

@@ -1,5 +1,6 @@
 pysrc = files(
     '__init__.py',
+    '__main__.py',
     'passgeny.py',
     'bhash.py',
     'phogen.py')