Add minifyStyles plugin, test and dependencies.

plugins/minifyStyles.js

@@ -0,0 +1,71 @@
+'use strict';
+
+exports.type = 'perItem';
+
+exports.active = true;
+
+exports.params = {
+  svgo: {}
+};
+
+exports.description = 'minifies existing styles in svg';
+
+var csso = require('csso');
+
+
+// wraps css rules into a selector to make it parseable
+var rulesToDummySelector = function(str) {
+    return '.dummy { ' + str + ' }';
+};
+
+// helper to extract css rules from full css selector
+var extractRuleCss = function(str) {
+    var strEx = str.match(/\.dummy{(.*)}/i)[1];
+    return strEx;
+};
+
+// minifies css using csso
+var minifyCss = function(css, options) {
+  return csso.minify(css);
+};
+
+
+
+/**
+  * Minifies styles (<style> element + style attribute) using svgo
+  *
+  * @param {Object} item current iteration item
+  * @return {Boolean} if false, item will be filtered out
+  *
+  * @author strarsis <strarsis@gmail.com>
+  */
+exports.fn = function(item, svgoOptions) {
+
+        if(item.elem) {
+          if(item.isElem('style')) {
+            var styleCss = item.content[0].text;
+            if(styleCss.length > 0) {
+              var styleCssMinified = minifyCss(styleCss, svgoOptions);
+              item.content[0].text = styleCssMinified;
+            }
+          }
+
+          if(item.hasAttr('style')) {
+            var itemCss = item.attr('style').value;
+            if(itemCss.length > 0) {
+              var itemCssMinified =
+                extractRuleCss(
+                  minifyCss(
+                    rulesToDummySelector(
+                      itemCss
+                    ),
+                    svgoOptions
+                  )
+                );
+              item.attr('style').value = itemCssMinified;
+            }
+          }
+        }
+
+        return item;
+};