Stacking text commands (#1009)

* Adding support for SansSerif-Bold

* Updating to include SansSerif Italic.

* WIP

* Working text stacking

* More robust screenshot.

* Don't want to break users :)

* Updating per PR comments.

* Fixing Unicode and updating snapshots.

* Adding suggested tests.

* Opting to use old method for unit testing.

* Adding TODO

static/katex.less

@@ -56,19 +56,39 @@
     .strut {
         display: inline-block;
     }
-
-    .mathrm {
-        font-style: normal;
+    
+    // Text font weights
+    .textbf {
+        font-weight: bold;
     }
-
+    
+    // Text font shapes.
     .textit {
         font-style: italic;
     }
+    
+    // Text font families.
+    .textrm {
+        font-family: KaTeX_Main;
+    }
+    
+    .textsf {
+        font-family: KaTeX_SansSerif;
+    }
+    
+    .texttt {
+        font-family: KaTeX_Typewriter;
+    }
 
+    // Math fonts.
     .mathit {
         font-family: KaTeX_Math;
         font-style: italic;
     }
+    
+    .mathrm {
+        font-style: normal;
+    }
 
     .mathbf {
         font-family: KaTeX_Main;