Handle CRLF

[bakkot]

We should handle Windows line endings somehow, either by explicitly supporting them in input (though presumably outputting them as just '\n') or (my preference) explicitly disallowing them, with a useful error message.

[michaelficarra]

What's the error message currently? Something like "Unexpected \r"?

[bakkot]

No, it's parsed as text.

[michaelficarra]

Oh god, yeah rejecting it with a nice error sounds good.