Add LESS support (.less)

Cheating slightly as it uses the CSS lexer, as pygments currently does
not have a dedicated less lexer. But I figure language recognition and
90% percent correct syntax highlighting is better than neither.

lib/linguist/languages.yml

@@ -731,6 +731,13 @@ Lasso:
   - .lasso9
   - .ldml
 
+Less:
+  type: markup
+  group: CSS
+  lexer: CSS
+  ace_mode: less
+  primary_extension: .less
+
 LilyPond:
   lexer: Text only
   primary_extension: .ly

samples/Less/screen.less

@@ -0,0 +1,14 @@
+@blue: #3bbfce;
+@margin: 16px;
+
+.content-navigation {
+  border-color: @blue;
+  color:
+    darken(@blue, 9%);
+}
+
+.border {
+  padding: @margin / 2;
+  margin: @margin / 2;
+  border-color: @blue;
+}