use Object.defineProperty to provide a Symbol.create impl, instead of an assignment.  fixes #161
Fixed an ES5 strict test that crashes in Chrome

The test `(function f() { f = 123; })()` actually throws a SyntaxError
on evaluation, not a TypeError on execution, in the current Chrome. I'm
really not sure which is fully correct for either the ES5 or ES6 specs.
Nevertheless, I've changed that line to be eval()ed so that the entire
script doesn't crash.

Also, the link to the strict mode page is fixed.
Merge pull request #196 from webbedspace/strictmode

Fixed an ES5 strict test that crashes in Chrome
Merge pull request #163 from toshok/Symbol.create-fix

use Object.defineProperty to provide a Symbol.create impl.  fixes #161
Build html files
Add exponentiation operator to ES7 table. Closes #179