Added event_time attr to the FileSystemEvent for more accurate timing…

[xzava]

Due to blocking their is a delay between when FileSystemEvent obj is created and when the FileSystemEventHandler processed the event. Is means you could only collect the time the event was handled, rather than the time it the event was created.

Events are processed one by one so any blocking on the FileSystemEventHandler affects the time.

So I added 'event_time' property to FileSystemEvent base class to accurately log the time the event was created.

>>> event
<FileModifiedEvent: event_type=modified, src_path='./watch2.py', is_directory=False, event_time=2021-01-19T12:51:29.821598>