Added CSS3 filter() mixin

doc-src/content/reference/compass/css3/filter.haml

@@ -0,0 +1,15 @@
+--- 
+title: Compass Filter
+crumb: Filter
+framework: compass
+stylesheet: compass/css3/_filter.scss
+meta_description: Specify the (image) filter for all browsers.
+layout: core
+classnames:
+  - reference
+  - core
+  - css3
+---
+- render 'reference' do
+  %p
+    The filter mixin is used to apply filters to images.

frameworks/compass/stylesheets/compass/_css3.scss

@@ -16,3 +16,4 @@
 @import "css3/appearance";
 @import "css3/regions";
 @import "css3/hyphenation";
+@import "css3/filter";

frameworks/compass/stylesheets/compass/css3/_filter.scss

@@ -0,0 +1,24 @@
+// Provides cross-browser support (Webkit, Mozilla, MSIE, and Opera)
+// Each filter argument should adhere to the standard css3 syntax for the
+// filter property.
+@mixin filter (
+  $filter-1 : default,
+  $filter-2 : false,
+  $filter-3 : false,
+  $filter-4 : false,
+  $filter-5 : false,
+  $filter-6 : false,
+  $filter-7 : false,
+  $filter-8 : false,
+  $filter-9 : false,
+  $filter-10: false
+) {
+  @if $filter-1 == default {
+    @warn "Using default filter: grayscale(100%)";
+    $filter-1: grayscale(100%);
+  }
+  $filter : compact($filter-1, $filter-2, $filter-3, $filter-4, $filter-5, $filter-6, $filter-7, $filter-8, $filter-9, $filter-10);
+  @include experimental(filter, $filter,
+    -moz, -webkit, -o, -ms, not -khtml, official
+  );
+}