make it possible to use harmony transforms in the browser with script tags

[zpao]

We already have the option enabled in the browser transform, and we export a function there that takes an option (for use with react-rails, et al). But we didn't make it possible to pass options from your <script type="text/jsx"> blocks. Let's do it.

Since there are no JS data types in html, let's just do an JSON.stringifyed data-options attribute.

There's only the single option right now, so <script type="text/jsx" data-options="{\"harmony\": true}" is all we need to support. Other options can be added easily if they come up.

[sophiebits]

Well, we could do type="text/jsx;harmony" or similar; that's used to specify JS language versions in Firefox.