Support comments in JSX

[zpao]

This should work:

<div>
  {/* this is a comment */}
</div>

But it doesn't. The fix for this will actually need to happen in https://github.com/facebook/esprima/tree/fb-harmony but I wanted to get it on file here so we can remember to call it out in the changelog.

[vjeux]

Things we also talked about:

• Adding <!-- comment --> that would be transformed into /* comment */
• We can already do the following but they are not optimal: {{/* comment */}}, {[/* comment */]}, {!/* comment /*0}
• Handlebar does the following: {{! comment }}
• Javascript comments are already working within the tag: <div /* comment */> and <div // comment \n>

[jeffmo]

Just an update: I've got a change to the parser queued up that allows for <div>{/* this is a comment*/}</div>.
I'll probably send it out tomorrow after I've had some time to do a little more extensive testing first...but it should do the trick