Support for rename

[alansingfield]

I've created a beta of supporting Rename at: https://github.com/alansingfield/YellowCounter.FileSystemState/tree/features/detect-renames

If it sees a pair of CREATE / DELETE events in the same directory which match on lastmodified / length, it is probably a rename. It also looks for this across subdirectories, but only if the filename matches.

I need to reinstate the serialisation of state function - however I'm not too keen on the binary serialization, might have a look at a json format or similar.