Solve Safari rendering issues with font-size overrides. (#780)

Some delicate surgery is required on the `vlist-s` table-cell CSS.
Problem with #768 reported by @ronkok; issue #779. Fixes:

* `font-size: 1px` (rather than `font-size: 0.05em`) solves render
  issues with user overrides of the `.katex` `font-size`.
* Also fix a width issue.

src/buildCommon.js

@@ -386,6 +386,9 @@ const makeVList = function(children, positionType, positionData, options) {
     }
 
     const vtable = makeSpan(["vlist-t"], rows);
+    if (rows.length === 2) {
+        vtable.classes.push("vlist-t2");
+    }
     vtable.height = maxPos;
     vtable.depth = -minPos;
     return vtable;

static/katex.less

@@ -241,12 +241,6 @@
         display: table-row;
     }
 
-    .vlist-s {
-        display: table-cell;
-        vertical-align: bottom;
-        font-size: 0.05em;
-    }
-
     .vlist {
         display: table-cell;
         vertical-align: bottom;
@@ -268,6 +262,23 @@
         }
     }
 
+    .vlist-t2 {
+        margin-right: -2px;
+    }
+
+    .vlist-s {
+        // This cell solves Safari rendering problems. It has text content, so
+        // its baseline is used for the table. A very small font avoids line-box
+        // issues; absolute units prevent user font-size overrides from breaking
+        // rendering. Safari refuses to make the box zero-width, so we give it
+        // a known width and compensate with negative right margin on the
+        // inline-table.
+        display: table-cell;
+        vertical-align: bottom;
+        font-size: 1px;
+        width: 2px;
+    }
+
     .msupsub {
         text-align: left;
     }