Unify configuration across platforms

[jmrohwer]

I've been looking at adding a configuration option for pandas, as per the discussion in #91.

The configuration system is currently kludgy, being different for Windows and POSIX. This is mostly legacy. I am suggesting unifying and consolidating this:

• os.path.expanduser('~') works on all platforms and on Windows evaluates to the same path as os.getenv('USERPROFILE'), which is used currenty
• the install location can be obtained with sysconfig.get_path('platlib') which works on all platforms.

@bgoli any objections to this or am I missing something? We would then not need separate configuration code for win32.

[bgoli]

Pre windows 9 or 10 os.path.expanduser('~') did not work as expected on Windows and was even worse if MinGW or similar was installed and I had to hack something else. Both work as expected on Win11 so I would say go for it.

[jmrohwer]

Implemented in #91