Support asctime field for timestamp

[morganchristiansson]

https://github.com/madzak/python-json-logger and other python json loggers tend to use asctime field.

This reflects the fieldname in python stdlib logging framework https://docs.python.org/3/library/logging.html

Would be great if asctime was automatically supported.

[aybabtme]

I'd love to support more formats! Do you have a PR for it?

[omerV81]

Seems to work right now (with argument --time-fields asctime), perhaps it was added?

[aybabtme]

This argument allows any custom key, yes. However I would like to automatically detect most commonly used timestamp keys. I'll keep this issue around as a reminder.