Scss Mixins Collection Versions Save

Now all spacing mixins can take second optional argument to be able to make unequal spacing values.
Example:

h2 {
  @include margin-h(10px, 20px);
}

h2 {
  margin-top: 10px;
  margin-bottom: 20px;
}

• Changed entry point to scss-mixins-collection/_index.scss
• Refactored file structure - now every mixin has its own file
• Removed not-so-useful or deprecated mixins
  • mixins that add vendor prefixes - use autoprefixer instead
  • background-gradient
  • device-z-index-fix
  • fullwidth
  • hack-bootstrap
  • on-state
  • reset-filter
  • touch-scroll
  • user-select
• Renamed mixins
  • multiline-ellipsis => ellipsis-multiline
  • multiline-ellipsis-simple => ellipsis-multiline-simple
  • responsive-image => fit-image

• add size($width, $height) mixin;
• add color reset for reset-link mixin;

• Added if-children mixin;
• Refactored mixins;
• Issues fix: 2, 3, 4;