Allow to check a io.Reader instead of raw file descriptor

[cardil]

The lib allows checking TTY versus a raw file descriptor. It would be convenient to allow checking of a given io.Reader instead, as pointed out by @dolmen in #80 (comment)

[dolmen]

I'm now fully against this feature as I explained here: #80 (comment)

This is just a convenience API and it is still possible to make this feature available in another package using go-isatty as backend.

[smokersaim]

I ran into this limitation too and ended up with probe, which supports TTY checks from io.Reader / io.Writer. Might be useful depending on your use case. Happy to discuss if there’s interest.