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

test/screenshotter/ss_data.yaml

@@ -33,7 +33,7 @@ Alignedat: |
         3a &= 3 & 17b &= 34 &\quad 400c &= 1200
     \end{alignedat}
 Arrays: |
-    \left(\begin{array}{|rl|c||}
+    \left(\begin{array}{|rl:c||}
         1&2&3\\
         1+1&2+1&3+1\cr1\over2&\scriptstyle 1/2&\frac12\\[1ex]
         \begin{pmatrix}x\\y\end{pmatrix}&0&\begin{vmatrix}a&b\\c&d\end{vmatrix}