Log Message:
py-multidict: updated to 4.7.1

4.7.1:

Bugfixes
- `CIMultiDictProxy.copy` return object type `multidict._multidict.CIMultiDict`
- Make `CIMultiDict` subclassable again
- Fix regression, multidict can be constructed from arbitrary iterable of pairs \ 
again.
- `CIMultiDict.add` may be called with keyword arguments

Improved Documentation
- Mention ``MULTIDICT_NO_EXTENSIONS`` environment variable in docs.
- Document the fact that ``istr`` preserves the casing of argument untouched but \ 
uses internal lower-cased copy for keys comparison.