Fix reload with custom logger

[Hanaasagi]

It will resolve #328, backport __reduce__ method from Python 3.7.

https://github.com/python/cpython/blob/29500737d45cbca9604d9ce845fb2acc3f531401/Lib/logging/__init__.py#L1730-L1736

    def __reduce__(self):
        # In general, only the root logger will not be accessible via its name.
        # However, the root logger's class has its own __reduce__ method.
        if getLogger(self.name) is not self:
            import pickle
            raise pickle.PicklingError('logger cannot be pickled')
        return getLogger, (self.name,)

[tomchristie]

Now resolved in master - thanks for your time on this!