Support `--side-by-side` switch

[rpdelaney]

I'm not getting diffr highlighting when using colordiff -y foo bar | diffr. Would be neat to support that also.

[mookid]

I assume that colordiff -y makes the splitting.

I think that the parsing would be too tedious to be honest. Another possibility would be to implement the side-by-side rendering in diffr, but it is out of reach given the capabilities of the terminal currently used.

Anyway, I would be very curious to see anyone giving that a try :)

[rpdelaney]

Yeah -y is short for --side-by-side. colordiff isn't necessary, that's just muscle memory on my part. GNU diff is the same.

I could give it a shot except rust isn't (yet) my jam.