Add command to fix stdin data

[or]

Addresses #255.

Command could also be called "pipe" or just "stdin".

[or]

Rebased on #257 to avoid merge/rebase conflicts later, so ignore the first commit.

This could be done without using fix-stdin and check-stdin, but I felt that convolutes fix and check, requiring branching based on stdin? regarding the status output.

Perhaps - could/should be mentioned in the --help output, but I didn't want to get creative with that.

Let me know what you think and if you have have preferred wording.

[abreumatheus]

Any prospects on this?

[weavejester]

I haven't yet made time to look at this. It's a difficult problem to solve well, and I'll need to give this some thought.