Adding replace function

lib/less/functions.js

@@ -218,6 +218,13 @@ tree.functions = {
     escape: function (str) {
         return new(tree.Anonymous)(encodeURI(str.value).replace(/=/g, "%3D").replace(/:/g, "%3A").replace(/#/g, "%23").replace(/;/g, "%3B").replace(/\(/g, "%28").replace(/\)/g, "%29"));
     },
+    replace: function (subject, pattern, replacement, flags) {
+        var str = subject.value;
+
+        str = str.replace(new RegExp(pattern.value, flags ? flags.value : ""), replacement.value);
+
+        return new(tree.Quoted)('"' + str + '"', str);
+    },
     '%': function (quoted /* arg, arg, ...*/) {
         var args = Array.prototype.slice.call(arguments, 1),
             str = quoted.value;

test/css/functions.css

@@ -45,6 +45,9 @@
   contrast-dark-thresh-per: #eeeeee;
   contrast-high-thresh-per: #eeeeee;
   contrast-low-thresh-per: #111111;
+  replace: "Hello, World!";
+  replace-captured: "This is a new string.";
+  replace-with-flags: "2 + 2 = 4";
   format: "rgb(32, 128, 64)";
   format-string: "hello world";
   format-multiple: "hello earth 2";

test/less/functions.less

@@ -49,6 +49,9 @@
   contrast-dark-thresh-per: contrast(#000, #111111, #eeeeee, 50%);
   contrast-high-thresh-per: contrast(#555, #111111, #eeeeee, 60%);
   contrast-low-thresh-per: contrast(#555, #111111, #eeeeee, 10%);
+  replace: replace("Hello, Mars.", "Mars\.", "World!");
+  replace-captured: replace("This is a string.", "(string)\.$", "new $1.");
+  replace-with-flags: replace("One + one = 4", "one", "2", "gi");
   format: %("rgb(%d, %d, %d)", @r, 128, 64);
   format-string: %("hello %s", "world");
   format-multiple: %("hello %s %d", "earth", 2);