Add a Sass function to convert pixels to rems (resolves #67)

[greatislander]

This pull request adds a function for converting pixels to rems as requested in #67. It uses the unitless example from CSS Tricks, so the following will both work:

body {
  font-size: rem(20);
}

body {
  font-size: rem(20px);
}

[tatianamac]

Thank you, @greatislander! This is so awesome and helpful.

@ovlb would love a second review here. I think we'll also want to open up an issue to ensure that we change all instances of px to rems using this function.

[greatislander]

@tatianamac Glad to contribute! I’m also happy to take care of the follow-up issue you mentioned, but I figured I would wait to let you review this before jumping ahead to converting everything to use the function :)

[ovlb]

One tiny thing regarding naming, otherwise everything works fine. Thanks, @greatislander!

If you want, just push the other px -> function replacements to this PR and we skip creating a follow-up issue :)

[greatislander]

Sounds good @ovlb!

[greatislander]

One other thought occurred to me — structurally, would there be some value in moving Sass functions and mixins into their own partials that are imported at the top of the base file?

[ovlb]

Great. Thanks :)

[ovlb]

One other thought occurred to me — structurally, would there be some value in moving Sass functions and mixins into their own partials that are imported at the top of the base file?

Yes, there definitely is. I started this work for the regular classes in #75 but skipped the Sass part, as I waited for this PR to get merged.
Any preference on how to do it? In other projects, I have a folder named _sass in which I collect such partials. But am open to suggestions :) If you want to do this, go ahead!

[greatislander]

@ovlb I think having _mixins.scss and _functions.scss partials in that _sass folder would make sense. I can move the function into such a partial in this PR — if you prefer I could make a separate one for the mixins so as to keep this PR within scope.

[ovlb]

@greatislander That sounds perfect, thanks!

[greatislander]

@ovlb Done!

[tatianamac]

Perfect!