BUG: missing pandas.version submodule

[rgommers]

The public pandas.version submodule seems to have been removed without any deprecation warning beforehand in gh-10370. This causes a number of test failures for statsmodels.

[jreback]

pandas.version was a private, undocumented version string module.

pandas.__version__ has always been (and is) the version tag. the module just implemented it (which is what changed here)

apologize @josef-pkt

[rgommers]

That's a very strange definition of private. Anything that doesn't start with an underscore and is in the main namespace is public simply by being there in pretty much any Python project I know. And in this case the write_version approach was simply copied from numpy/scipy, where the version module is definitely public.

But well, it's up to you to decide here...