Underscore problem unsolved

[bondjimbond]

Under "Dealing with underscores" in the README, the filename_separator parameter theoretically solves the "datastreams with underscores" problem, but not so for users working in MacOS.

Using filename_separator requires that the PID in the filename use the colon character instead of the underscore. But MacOS will not allow you to save files with the colon character.

[bondjimbond]

Actually, it looks like you can't safe filenames with colons in them, either.

What we really need is to be able to set a value like pid_separator along side filename_separator, so that we can do this right.