Move htmltojsx.js to React-Magic project.

The HTMLtoJSX file is really a part of the React-Magic project, and should belong there rather than here:
 - It doesn't really follow the release cycle of React at all
 - It is totally standalone with no dependency on React
 - The only usage of this script is in React-Magic and on the HTML to JSX page on the React website (http://facebook.github.io/react/html-jsx.html)

I've hotlinked it from the Github site for that project since this was the easiest way to pull it in.

Due to the fact that Github Pages is like Geocities in that it lacks redirects (among other basic web hosting functionality), I've replaced the `html-jsx-lib.js` file with a comment explaining where the file has moved to, just in case anyone was hotlinking it from the React site.