Make modules private

[tobinus]

Right now, it is entirely possible to do something like:

from podgen.podcast import Podcast

instead of the intended:

from podgen import Podcast

This is problematic because code which uses PodGen may rely on the module names and module contents being the way they are now. It is therefore more challenging to make changes to the inner organization of PodGen.

In new minor version:

• Change name of modules so they start with an underscore
• Create aliases under the old public names which make available the same contents as before (to preserve backwards compatibility)
• Emit DeprecationWarning when the aliases are run (i.e. imported)

In new major version:

• Remove the aliases.