Support Unicode delimiters (#1207)

* Support Unicode delimiters

This PR adds support for the Unicode versions of \lfloor, \rfloor, \lceil, \rceil, \lgroup, \rgroup, \lmoustache, \rmoustache, \ulcorner, \urcorner, \llcorner, and \lrcorner.

All the mappings agree with `unicode math`

* Change tests from Parse to Build

test/katex-spec.js

@@ -2960,6 +2960,15 @@ describe("Unicode", function() {
     it("should parse binary operators", function() {
         expect("±×÷∓∔∧∨∩∪≀⊎⊓⊔⊕⊖⊗⊘⊙⊚⊛⊝⊞⊟⊠⊡⊺⊻⊼⋇⋉⋊⋋⋌⋎⋏⋒⋓⩞\u22C5").toParse();
     });
+
+    it("should parse delimeters", function() {
+        expect("\\left\u230A\\frac{a}{b}\\right\u230B").toBuild();
+        expect("\\left\u2308\\frac{a}{b}\\right\u2308").toBuild();
+        expect("\\left\u27ee\\frac{a}{b}\\right\u27ef").toBuild();
+        expect("\\left\u27e8\\frac{a}{b}\\right\u27e9").toBuild();
+        expect("\\left\u23b0\\frac{a}{b}\\right\u23b1").toBuild();
+        expect("┌x┐ └x┘").toBuild();
+    });
 });
 
 describe("The maxSize setting", function() {