Padding over \sqrt and Paths for frac-line (#1143)

* Padding over \sqrt and Paths for frac-line

This replaces two earlier PRs.

* Restore reaction arrows

* regenerate screenshots

* Set line padding in a constant

* Update with latest master

* Fix lint error

* update screenshots

src/katex.less

@@ -413,7 +413,9 @@
             display: inline-block;
             margin: 0 -0.125em;     // The ink in the rule is actually 0.05em wide.
             width: 0.25em;          // We put it in a 0.25em wide span to overcome
-        }                           // a Chrome rendering issue.
+            overflow: hidden;       // a Chrome rendering issue.
+            position: relative;
+        }
 
         .arraycolsep {
             display: inline-block;
@@ -475,6 +477,8 @@
     .stretchy {
         width: 100%;
         display: block;
+        position: relative;
+        overflow: hidden;
 
         &:before,
         &:after {