Add $offset parameter to rhythm() function.

[JohnAlbin]

I was writing a mixin that needed to subtract a couple pixels from the vertical rhythm margin, just like the rhythm borders mixins do.

And then I noticed the math the rhythm border mixins are using is almost identical to the math in the rhythm() function.

Keeping with DRY, I'd like to propose we add an $offset parameter to the rhythm() function.

Then I can use rhythm() in my mixin instead of copy/pasting/rewriting lines of code from the rhythm borders mixins.

Note that the $offset parameter is totally backwards compatible with existing usage of the rhythm() function. No one's existing Sass should be affected.

[mirisuzanne]

Love it. +1

[ry5n]

Awesome! Would be handy in other cases, eg. creating a mixin that shifts an element 'out of phase' (like a heading with more space above and correspondingly less space below) while maintaining the rhythm.

[mirisuzanne]

missing a comma at the end of this line.

[JohnAlbin]

And I added a semi-colon after $offset: 0! Not sure how I managed both of those errors. :-p

Fixed them up and pushed a new commit.