* Added/fleshed out docstrings on file, classes and functions.
* No need to use a function for the stack frame getting.
* Check if LogRecord has class or qualname before setting, allowing
upstream to implement them.
* Use setattr()/getattr() rather than __dict__ fiddling.
* Force an error string into class/qualname if we have issues finding
them, rather than failing silently to ''.
* Also now providers single caller_class_and_qualname() method to get
both strings, returned as a Tuple[str, str]. Either could be empty
if something went wrong.
* Rather than a fragile 'skip' this now:
1. Looks for the first up-stack frame with self of logging.Logger
1. Then looks for the next up-stack frame with self NOT of
logging.Logger. This should be the call site we want.
