Compare with a few commits back, not just the last commit

[leotrs]

This is a great project! Is it possible to apply darker to the lines modified since a few commits back, instead of just comparing to the last commit?

[leotrs]

Woops, just found the -r flag. This is awesome!

[akaihola]

Thanks @leotrs! The -r/--revision flag is quite a new thing – please come back with feedback if you find any flaws in how it works. Also, if it isn't well explained in the documentation, I'd consider that a documentation bug worth fixing.