Support \origof and \imageof (#2283)

* Support \origof and \imageof

* Fix documentation table

Co-authored-by: ylemkimon <mail@ylem.kim>

test/katex-spec.js

@@ -3558,6 +3558,11 @@ describe("Unicode", function() {
         expect`∈∋∝∼∽≂≃≅≈≊≍≎≏≐≑≒≓≖≗≜≡≤≥≦≧≪≫≬≳≷≺≻≼≽≾≿∴∵∣≔≕⩴⋘⋙⟂⊨∌`.toBuild(strictSettings);
     });
 
+    it("should parse relations", function() {
+        // These characters are not in the KaTeX fonts. So they build with an error message.
+        expect`⊶⊷`.toParse();
+    });
+
     it("should build big operators", function() {
         expect`∏∐∑∫∬∭∮⋀⋁⋂⋃⨀⨁⨂⨄⨆`.toBuild(strictSettings);
     });