Added 'extends null' class test.
Added accessor properties subtests to the class test.

Also fixed a bug with EJS's results for WeakMap#delete and WeakSet#delete.
Added additional rest parameter tests.

The results for IE11TP are not confirmed.
Reassigned EchoJS as an engine, not an ES6->ES5 compiler.

Closes #362. Note that this commit does not change es6/index.html, to avoid merge conflicts with my other pull requests. A fresh compile should be done after all of them are accepted.
Merge pull request #363 from webbedspace/fix

Added extra class and rest parameter tests
Merge pull request #365 from webbedspace/ejs

Reassigned EchoJS as an engine, not an ES6->ES5 compiler.
Added computed property destructuring test.
Updated Firefox results for computed destructuring.
Merge pull request #366 from webbedspace/computed-destructuring

Added computed property destructuring test
new ejs data (weakmap/weakset/misc others)