At the top level, AnyQt exports a Qt5 compatible module namespace along with
some minimal renames to better support portability between different
versions.
The "QT_API" environment variable controls which Qt API/backend is used.
The API can be chosen/forced programmatically (as long as no
PyQt4/PyQt5/PySide was already imported).
An optional compatibility import hook that denies imports from
conflicting Qt APIs, or intercepts and fakes Qt4 API imports to use a Qt5
compatible API (some monkey patching is involved).