Add ZBase32 encoding function

See: https://tools.ietf.org/html/rfc6189#section-5.1.6

test/general/util.js

@@ -165,4 +165,11 @@ describe('Util unit tests', function() {
     });
   });
 
+  describe("Zbase32", function() {
+    it('util.encodeZBase32 encodes correctly', function() {
+      const encoded = openpgp.util.encodeZBase32(openpgp.util.str_to_Uint8Array('test-wkd'));
+      expect(encoded).to.equal('qt1zg7bpq7ise');
+    })
+  })
+
 });