Dart Sass 1.0.0-alpha.5

• Fix bounds-checking for opacify(), fade-in(), transparentize(), and fade-out().
• Fix a bug with @extend superselector calculations.
• Fix some cases where #{...}-- would fail to parse in selectors.
• Allow a single number to be passed to saturate() for use in filter contexts.
• Fix a bug where **/ would fail to close a loud comment.
• Fix a bug where mixin and function calls could set variables incorrectly.
• Move plain CSS @imports to the top of the document.