stdin

[OliverJAsh]

This would be useful for sharing reduced test cases and experimenting, so we can't have to create files on disk.

I believe we used to have this?

[samhh]

We stopped taking stdin here:

This is closer to the likely eventual interface of receiving a glob of files.

Which is referencing #25.

I think we could add stdin/stdout support for an individual input without breaking forwards-compatibility with #25.

Accepting stdin via the CLI parser is a bit fiddly as evidenced by tshm.

[samhh]

This relates a bit to #129.