.log to print success value

[nfx]

For those, who have to support existing parsers written with fastparse, it would be a very nice idea to add fastparse.ParsingRun#successValue to fastparse.LogByNameOps#log output, e.g.

-primary:1:1:Success(1:2, cut) => Integer(1)

Printing only the first 64 characters of string representation would make the most sense.