Upgrade to Susy 3 and replace grid mixins with new span and gutter functions

Most of Susy's mixins have been deprecated, `@include container()`, `@include full()`, `@include span()`, `@include prefix()`, `@include suffix()`, `@include gallery()`, etc.

Fixes #1114

_sass/minimal-mistakes/vendor/susy/susy/_su-validate.scss

@@ -0,0 +1,213 @@
+/// Validation
+/// ==========
+/// Each argument to Su has a single canonical syntax.
+/// These validation functions check to ensure
+/// that each argument is valid,
+/// in order to provide useful errors
+/// before attempting to calculate the results/
+///
+/// @group x-validation
+///
+/// @see su-valid-columns
+/// @see su-valid-gutters
+/// @see su-valid-spread
+/// @see su-valid-location
+
+
+
+// Valid Span
+// ----------
+/// Check that the `span` argument
+/// is a number, length, or column-list
+///
+/// @group x-validation
+///
+/// @param {number | list} $span -
+///   Number of columns, or length of span
+///
+/// @return {number | list} -
+///   Validated `$span` number, length, or columns list
+///
+/// @throw
+///   when span value is not a number, or valid column list
+@function su-valid-span(
+  $span
+) {
+  $type: type-of($span);
+  @if ($type == 'number') {
+    @return $span;
+  } @else if ($type == 'list') and su-valid-columns($span, 'silent-failure') {
+    @return $span;
+  }
+
+  $actual: '[#{type-of($span)}] `#{inspect($span)}`';
+  @return _susy-error(
+    '#{$actual} is not a valid number, length, or column-list for $span.',
+    'su-valid-span');
+}
+
+
+
+// Valid Columns
+// -------------
+/// Check that the `columns` argument is a valid
+/// list of column-lengths
+///
+/// @group x-validation
+///
+/// @param {list} $columns -
+///   List of column-lengths
+/// @param {bool} $silent-failure [true] -
+///   Set false to return null on failure
+///
+/// @return {list} -
+///   Validated `$columns` list
+///
+/// @throw
+///   when column value is not a valid list of numbers
+@function su-valid-columns(
+  $columns,
+  $silent-failure: false
+) {
+  @if (type-of($columns) == 'list') {
+    $fail: false;
+
+    @each $col in $columns {
+      @if (type-of($col) != 'number') {
+        $fail: true;
+      }
+    }
+
+    @if not $fail {
+      @return $columns;
+    }
+  }
+
+  // Silent Failure
+  @if $silent-failure {
+    @return null;
+  }
+
+  // Error Message
+  $actual: '[#{type-of($columns)}] `#{inspect($columns)}`';
+
+  @return _susy-error(
+    '#{$actual} is not a valid list of numbers for $columns.',
+    'su-valid-columns');
+}
+
+
+
+// Valid Gutters
+// -------------
+/// Check that the `gutters` argument is a valid number
+///
+/// @group x-validation
+///
+/// @param {number} $gutters -
+///   Width of a gutter
+///
+/// @return {number} -
+///   Validated `$gutters` number
+///
+/// @throw
+///   when gutter value is not a number
+@function su-valid-gutters(
+  $gutters
+) {
+  $type: type-of($gutters);
+
+  @if ($type == 'number') {
+    @return $gutters;
+  }
+
+  $actual: '[#{$type}] `#{inspect($gutters)}`';
+  @return _susy-error(
+    '#{$actual} is not a number or length for $gutters.',
+    'su-valid-gutters');
+}
+
+
+
+// Valid Spread
+// ------------
+/// Check that the `spread` argument is a valid
+/// intiger between `-1` and `1`
+///
+/// @group x-validation
+///
+/// @param {0 | 1 | -1} $spread -
+///   Number of gutters to include in a span,
+///   relative to the number columns
+///
+/// @return {0 | 1 | -1} -
+///   Validated `$spread` number
+///
+/// @throw
+///   when spread value is not a valid spread
+@function su-valid-spread(
+  $spread
+) {
+  @if index(0 1 -1, $spread) {
+    @return $spread;
+  }
+
+  $actual: '[#{type-of($spread)}] `#{inspect($spread)}`';
+  @return _susy-error(
+    '#{$actual} is not a normalized [0 | 1 | -1] value for `$spread`.',
+    'su-valid-spread');
+}
+
+
+
+// Valid Location
+// --------------
+/// Check that the `location` argument is a valid number,
+/// within the scope of available columns
+///
+/// @group x-validation
+///
+/// @param {number} $span -
+///   Number of grid-columns to be spanned
+/// @param {integer | string} $location -
+///   Starting (1-indexed) column-position of that span
+/// @param {list} $columns -
+///   List of available columns in the grid
+///
+/// @return {integer} -
+///   Validated `$location` intiger
+///
+/// @throw
+///   when location value is not a valid index,
+///   given the context and span.
+@function su-valid-location(
+  $span,
+  $location,
+  $columns
+) {
+  $count: length($columns);
+
+  @if $location {
+    @if (type-of($location) != 'number') or (not unitless($location)) {
+      $actual: '[#{type-of($location)}] `#{$location}`';
+      @return _susy-error(
+        '#{$actual} is not a unitless number for $location.',
+        'su-valid-location');
+    } @else if (round($location) != $location) {
+      @return _susy-error(
+        'Location (`#{$location}`) must be a 1-indexed intiger position.',
+        'su-valid-location');
+    } @else if ($location > $count) or ($location < 1) {
+      @return _susy-error(
+        'Position `#{$location}` does not exist in grid `#{$columns}`.',
+        'su-valid-location');
+    } @else if ($location + $span - 1 > $count) {
+      $details: 'grid `#{$columns}` for span `#{$span}` at `#{$location}`';
+      @return _susy-error(
+        'There are not enough columns in #{$details}.',
+        'su-valid-location');
+    }
+  }
+
+  @return $location;
+}