Make it possible to log asynchronously

[erik-kallen]

I think it would be a nice feature if it were possible to specify that the actual should take place on a background thread.

If you like the feature, I can probably do it myself and create a PR.

[rupeshprasad]

i see it as a advantage. I am running into a weird issue with web application. Somehow it sends the log to blob or table after some time. It is not instant like file system where it logs right away. I think it is waiting for all thread to run before it can send the batch to table or process all events to blob.