Add llap and rlap

Summary:
By the powers of Greyskull (and maybe css) we have vanquished the
great and powerful llap! All hail!

Test Plan: Add some \llap and \rlap. Make sure it's positioned correctly.

Reviewers: spicyj

Reviewed By: spicyj

Differential Revision: http://phabricator.benalpert.com/D48

MJLite.js

@@ -80,6 +80,12 @@ var buildGroup = function(group, prev) {
 
             return makeSpan("mord mspace " + spacingClassMap[group.value]);
         }
+    } else if (group.type === "llap") {
+        var inner = makeSpan("", buildExpression(group.value));
+        return makeSpan("llap", inner);
+    } else if (group.type === "rlap") {
+        var inner = makeSpan("", buildExpression(group.value));
+        return makeSpan("rlap", inner);
     } else {
         console.log("Unknown type:", group.type);
     }

lexer.js

@@ -25,7 +25,7 @@ var funcs = [
     // Colors
     'blue', 'orange', 'pink', 'red', 'green', 'gray', 'purple',
     // Other functions
-    'dfrac'
+    'dfrac', 'llap', 'rlap'
 ];
 var anyFunc = new RegExp("^\\\\(" + funcs.join("|") + ")(?![a-zA-Z])");
 

parser.jison

@@ -90,6 +90,10 @@ func
         {$$ = [{type: 'color', value: {color: 'purple', value: $2}}];}
     | 'dfrac' group group
         {$$ = [{type: 'dfrac', value: {numer: $2, denom: $3}}];}
+    | 'llap' group
+        {$$ = [{type: 'llap', value: $2}];}
+    | 'rlap' group
+        {$$ = [{type: 'rlap', value: $2}];}
     ;
 
 atom

static/mjlite.css

@@ -129,6 +129,20 @@ big parens
     width: 2em;
 }
 
+.llap, .rlap {
+    width: 0;
+    position: relative;
+}
+
+.llap > span {
+    position: absolute;
+    right: 0;
+}
+
+.rlap > span {
+    position: absolute;
+    left: 0;
+}
 
 .mord.blue { color: #6495ed; }
 .mord.orange { color: #ffa500; }