Allow comma-delimited and nested lists for rem()
Fix typo
Only convert units if use-px-fallback is set
Merge branch 'master' into list-rems

* master:
  Bump version to 1.0.0.alpha.18.
  Bump version to 1.0.0.alpha.17.
  Bump Sass version dependency.
  Had this str-index function backwards.
  Handle checking for the stylesheet root by defining a custom function.
  Deprecate random because it's provided by Sass now.
  Bump import-once version.
  Changed gradient direction from to bottom to to top (... hah)
  Fixed syntax for linear-gradient
Merge pull request #1523 from chriseppstein/list-rems

Allow comma-delimited and nested lists for rem()