Feature request: Add support for passing --print-stats to only -c tarsnap calls

[estan]

Giving -o print-stats (or anything that affects output, like -o v) to tarsnapper seems to confuse the parsing that tarsnapper does of some of the tarsnap commands. It would be great if there was a tarsnapper specific print-stats config file option and command line flag that would only pass --print-stats to the tarsnap -c command (the output from which is not parsed).

[jeffwidman]

Perhaps the addition of pexpect in #29 can be leveraged to support this as well?

I haven't worked with pexpect, but @psde might know more...