Provide a way to override logging config

[vamshiaruru-virgodesigns]

Hi all,
Firstly, great project! I am looking forward to using this in one of my projects.
One thing that would be really good to have is the ability to override the logging config like gunicorn allows you to do. In gunicorn, you can provide a logconfig_dict which lets you specific file path, date format, date formats etc. It would be really good to have this here as well.
I don't think it would be very hard to implement it. I see the config is hard coded here

granian/granian/log.py

Line 26 in d69da15

LOGGING_CONFIG = {

, if we can provide an option to read this - and other command line arguments from a json/toml file, that would be enough.