update docs

README.mkdn

@@ -47,7 +47,7 @@ $grid-padding   : $gutter-width;  /* 1em padding on the grid */
 
 The basic grid is composed using two simple mixins:
 * Apply the `container` mixin to create your initial grid context. 
-* Apply the `columns` mixin to declare the width of an element on the grid.
+* Apply the `span-columns` mixin to declare the width of an element on the grid.
 
 Use the 'omega' trigger to declare elements that span the _final_ column of 
 their parent element, and pass a 'context' in nested situations. The 
@@ -66,13 +66,13 @@ For example:
   header { ... }
   */
 
-  nav { @include columns(3); }
+  nav { @include span-columns(3); }
 
   #content { 
-    @include columns(9 omega);
+    @include span-columns(9 omega);
 
-    #main { @include columns(6,9); }
-    aside { @include columns(3 omega,9); }
+    #main { @include span-columns(6,9); }
+    aside { @include span-columns(3 omega,9); }
   }
 
   footer { clear: both; }

REFERENCE.mkdn

@@ -63,8 +63,8 @@ $grid-padding   : $gutter-width   !default;
   - Default: `$total-columns`.
 
 ```scss
-nav { @include columns(3,12); }
-article { @include columns(9 omega,12); }
+nav { @include span-columns(3,12); }
+article { @include span-columns(9 omega,12); }
 ```
 **Span Columns**: `span-columns(<$columns> [<omega> , <$context>, <$from>])`
 - _Apply to any element to align it with the Susy Grid._
@@ -76,7 +76,7 @@ article { @include columns(9 omega,12); }
 
 ```scss
 .gallery-image { 
-  @include columns(3,9);              // each gallery-image is 3 of 9 cols.
+  @include span-columns(3,9);         // each gallery-image is 3 of 9 cols.
   &:nth-child(3n) { @include omega; } // every third image completes a row.
 }
 ```