fix typo in filename: logger_han*ld*er.py to logger_han*dl*er.py

[yoki]

There is an annoying typo in a filename. logger_hanlder.py should be named as logger_handler.py. Everywhere else, including docs referring to the file, calls handler as "handler", not "hanlder". Maybe it is even better to use "logging_handler.py", as in the docs

This is a breaking change. So we may want to start with a depreciation warning.