Added ability to create a dashed vertical line in arrays, using ':' (#1395)

* hacked together a dashed vertical bar

* Updated tests and spec.

* tidied up the screenshot template for arrays

* added the vertical lines at the end back

* Updated screenshots for arrays

src/katex.less

@@ -405,6 +405,10 @@
             border-right: 0.05em solid;
         }
 
+        .vs-dashed {
+            border-right: 0.05em dashed;
+        }
+
         .arraycolsep {
             display: inline-block;
         }