Make large fractions actually work

Summary:
Also, rename it to '\dfrac', because it's more like a display fraction

Auditors: spicyj

MJLite.js

@@ -51,8 +51,8 @@ var buildGroup = function(group, prev) {
         return makeSpan("mopen", textit(group.value));
     } else if (group.type === "close") {
         return makeSpan("mclose", textit(group.value));
-    } else if (group.type === "frac") {
-        var numer = makeSpan("mfracnum", buildExpression(group.value.numer, numer));
+    } else if (group.type === "dfrac") {
+        var numer = makeSpan("mfracnum", makeSpan("", buildExpression(group.value.numer, numer)));
         var mid = makeSpan("mfracmid", makeSpan());
         var denom = makeSpan("mfracden", buildExpression(group.value.denom, denom));
 

lexer.js

@@ -13,7 +13,7 @@ var normals = [
 ];
 
 var funcs = [
-    'cdot', 'frac', 'lvert', 'rvert', 'pm', 'div'
+    'cdot', 'dfrac', 'lvert', 'rvert', 'pm', 'div'
 ];
 var anyFunc = new RegExp("^\\\\(" + funcs.join("|") + ")(?![a-zA-Z])");
 

parser.jison

@@ -48,8 +48,8 @@ func
         {$$ = [{type: 'bin', value: yytext}];}
     | 'div'
         {$$ = [{type: 'bin', value: yytext}];}
-    | 'frac' group group
-        {$$ = [{type: 'frac', value: {numer: $2, denom: $3}}];}
+    | 'dfrac' group group
+        {$$ = [{type: 'dfrac', value: {numer: $2, denom: $3}}];}
     | 'lvert'
         {$$ = [{type: 'open', value: yytext}];}
     | 'rvert'

static/style.css

@@ -104,3 +104,8 @@ input {
     height: 0.05em;
     min-height: 1px;
 }
+
+.mfracnum > span {
+    display: inline-block;
+    vertical-align: bottom;
+}